The Physics in Hurdling

When training for a hurdles event, it is crucial to have an even running tempo, so that the number of steps between hurdles can be calculated. If the hurdler "stutter-steps", or takes a series of smaller steps in the approach, he/she will lose momentum, and therefore the take-off speed after the hurdle will be slower, and the race ultimately lost.

The average take-off distance is six to seven feet from the base of the hurdles. By taking off a long way in front of the hurdles, it is possible to obtain a large range while maintaining a low vertical height. The hurdler lands approximately three feet (1 meter) past the hurdle, so maximum height must be reached before clearing the hurdle. This also ensures a faster take-off time, as there is less time in the air, where there is not horizontal velocity gained.

The motion of hurdling over the object is an example of projectile motion where a person will jump at a certain launch angle and land at that same angle on the other side of the hurdle. For hurdling, the smaller the angle of take off, the less time it will take to pass over the hurdle but also with a smaller angle comes a greater distance covered. One must make sure to reach a height over the hurdle but not too high over the hurdle that you gain "hang time" and lose a precious second.

Right before the hurdle your knees act like springs and compress a certain distance, build energy (this is called potential energy of a spring), and release it into kinetic energy over the hurdle. When landing, the springs that are your knees take the impact, conserve the energy once again, and release it towards your run.

Physics Fun Fact of the Day - May 31

Rotational speed around the Earth is also dependent on altitude above sea level, and a person at the top of a mountain on the Equator is actually traveling faster than 1,660 km/hr (as he has further to go with each revolution).

Physics Fun Fact of the Day - May 30

A person on the equator is rotating around the Earth at about 1,660 km/hr.

Physics Fun Fact of the Day - May 29

Electricity doesn't move through a wire but through a field around the wire.

Basketball - Spin on the Ball

Spinning the ball when you shoot is not done to affect air resistance, or to make air resistance cause the ball's path to curve, as is the case in baseball. Basketballs move too slowly for that to happen. Once the basketball leaves the shooter's hand, it travels in an unchanging parabolic path. So what's the purpose of backspin? Backspin on the ball is used to help it to bounce into the net when it hits the rim. It will usually hit something, unless the throw was very high. The backspin, after contact with the back rim or board, will result in a change in velocity opposite to the spin direction, changing an equal-angle rebound into a velocity more toward the net. This makes it more likely that the ball will go in.

The Forces in Running

If one were to make a free body diagram of a person while he or she is sprinting, there would be many forces acting upon him or her. First would be the weight force from the pull of gravity, the applied force from one's muscles moving in a direction to the right, friction going opposite of the applied along with drag, and a normal force opposite the weight force. All of these forces together would add up to a runner's acceleration.

Physics Fun Fact of the Day - May 28

A whip makes a cracking sound because its tip moves faster than the speed of sound.

Baseball - The Knuckleball

A knuckleball is a pitch thrown by a pitcher which does not spin and seemingly dances towards the plate. Its name comes from how it is thrown, with the knuckles instead of with the whole finger. It dances because with the "little rotation, asymmetric stitch configurations can be generated that lead to a large imbalance of forces and extraordinary excursions in trajectory." Since the ball is thrown with little velocity (usually a speed around 60-65 mph), the ball has more time to "dance" its way to the plate. Also, the fact that drag is actually more on a smooth ball rather than a rough ball (like a baseball), the ball has more of an opportunity to dance its way towards the batter. The problem that pitchers, catchers, and batters have (also its effectiveness), is that no one knows where it will possibly go. This results in many walks by the pitcher, passed balls (errors by the catcher), and horrible-looking swings by the batter.

Physics Fun Fact of the Day - May 27

When a solid body is totally or partially immersed in a liquid, it experiences an apparent loss of weight.

This is equal to the weight of the liquid displaced by the solid. This apparent loss of weight is due to the upward force exerted by the liquid on the solid. This upward force is called the force of buoyancy.

The Advantage of Gravity

Gravity seems to pull us down and keep us in place while we run and come up. Up and down movement can be minimized by leaning the body forward while running. Such movement adds more horizontal component to the energy usage and, thus, contributes to a faster running speed with less energy expended.This trick is found in the way a runner leans but not with the waist but with the ankles. This lean gives a greater value to the x-component of the wait force giving the runner a bigger push in the direction he or she is running.

Physics Fun Face of the Day - May 26

Venus is the only planet that spins in the opposite direction to Earth.

The Magic (well physics) of Running

When competing in a race, the least amount of time possible wins. To achieve this one must know what to do. For example, the speed of a runner is determined by the distance traveled with each stride (stride length) and the number of strides taken in a given amount of time (stride frequency, sometimes also called cadence like music yay). Stride length times stride frequency equals speed (SL x ST = SPEED). For instance, five ft (1.5 m) per stride times three strides per second equals a speed of 15 ft (4.5 m) per second. To increase one's speed, a runner must simply increase one part without causing the other parameter to be reduced by a large amount. For instance, to increase the stride frequency to four strides per second by reducing the stride length to 4 ft (1.2 m) per stride would result in a speed of 16 ft (4.8 m) per second.

The length of each stride taken by a runner is considered the sum of three separate distances. The takeoff distance is the horizontal distance that the body's center of mass (CoM) is ahead of the toe of the front (leading) foot at the instant the rear (trailing) foot leaves the ground. The flight distance is the horizontal distance that the body's CoM travels while the runner is in the air. The landing distance is the horizontal distance that the toe of the leading foot is ahead of the CoM at the instant the runner lands. These distances can also be further broken down to speed of release, height of release, angle of release, and air resistance.

The frequency of each stride involves the time of the stride, which can be broken down to time on the ground and time in the air. During running, each foot contacts the ground for only a brief amount of time. At that moment, an impulsive force powers the body along a parabolic trajectory until the opposite foot touches the ground unlike walking where the trajectory is more circular. At the instant that the foot leaves the ground, the vertical (upward) component of velocity for the body's CoM should be equal to its horizontal (forward) velocity in order to produce maximum range before the opposite foot hits the ground. Energy is depleted in raising the body's CoM for each stride. This energy is not recovered when the CoM is lowered again. The more that the up and down movement is minimized, the smaller amount of energy will be expended in motion that is not used to move forward. In order to further minimize expenditure of wasted energy, both the arms and legs should be bent as much as possible. Hands and arms are swung from the shoulders and feet and legs are swung from the hips, similar to the swinging of a pendulum (from fingertip to shoulders and toe to hip). This arrangement is based on the principle of conservation of mechanical energy. As a result, the speed of a runner is directly related to the height of swinging objects (such as the length of arms and legs). If the arms and legs are bent while running, such positioning moves the CoM upward, which translates to a faster pace without increasing the amount of energy expended. This application of physics is the reason why runners run with their arms bent at the elbows, while holding their hands close to their waists, and why knees are bent as much as possible and shins are positioned parallel to the ground whenever the legs are swung forward.

Physics Fun Fact of the Day - May 25

Uranus is the only planet in our solar system that rolls on its side like a barrel.

Physics Fun Face of the Day - May 24

Water can work against gravity, moving up narrow tubes in a process called capillary action.

Physics Fun Fact of the Day - May 23

Sound travels at a speed of around 767 miles per hour.

Basketball - Receiving a Pass

The impact of a hard pass can be lessened, making it less likely the ball will knock the wind out of you, if it is caught into the body. The ball coming at you has momentum, m·v. By increasing the time over which you decelerate the ball, you lessen the force. In other words, since m·v = F·t, then F = (m·v) / t ... increasing t causes F to get smaller. This is the same principle that makes an air bag in your car work. The time over which you decelerate is lengthened, resulting in a lower force. Of course, catching a ball into your chest has other benefits. It makes it less likely you'll drop the ball, and harder for someone to grab.

Physics Fun Fact of the Day - May 22

Light from the Earth takes just 1.255 seconds to reach the Moon.

Physics Fun Fact of the Day - May 21

Electric eels can stun both predators and prey with electric shocks of around 500 volts.

Physics Fun Fact of the Day - May 20

Because of differences in gravity, a 220 lb. person would only weigh 84 lbs. on Mars.

Physics Fun Fact of the Day - May 19

On a clear day, a beam of sunlight can be reflected off a mirror and seen up to 40km away.

Basketball - Dribbling the Ball

The more air pressure a basketball has inside it, the less its surface will bend or deform during a bounce, and the more its original energy will be stored in the compressed air inside. Air stores and returns energy more efficiently than the material that the ball is made from. If the ball is underinflated, some of its energy is wasted in deforming the ball as it bounces, and the ball will not rebound very high. For the most elastic collision possible between the ball and the floor, you want a highly pressurized ball. (But you knew that already, didn't you! Now you know why!)The material you bounce the ball on is also very important. Think about how high it would bounce on a carpeted floor. A soft floor material will flex when the ball hits it, and this will steal some of the ball's energy. Clearly the harder the surface, the better.

Physics Fun Fact of the Day - May 18

Due to gravitational effects, you weigh slightly less when the moon is directly overhead.

Physics Fun Fact of the Day - May 17

If an item moves very, very fast, it becomes smaller and heavier.

Physics Fun Fact of the Day - May 16

Many physicists believe wormholes (a "shortcut" through space and time) exist all around us but they are smaller than atoms.

Baseball - Air Resistance

If a baseball is traveling at a speed at or less than 50 mph, the air flow around the ball is relatively smooth (assuming that there is little or no wind). Interesting enough, there is a layer surrounding the ball (same conditions apply) so that if there were a bug (or any other object for that matter) on the ball, they would not even feel the slightest breeze hit them while the ball travels at the speed of a fast-moving car. This layer loses area of the "impenetrable invisible layer" up until around 200 mph where the layer is totally nonexistent. Therefore, the flight of the ball is hardly altered if it is traveling at a speed of 50 mph, but as its speed increases from this magical number of 50 mph, the path the ball has to take becomes much more turbulent.

Also factoring into the force of air resistance that the ball feels is the spin that it holds. The stitching on the ball makes the drag depend on the position of the axis of rotation with respect to its stitch pattern, the direction of this axis with ground and the direction of the flight of the ball, and the velocity of the rotation of this ball. Because of this factor and the factors named in the first paragraph, if you were to throw a 90 mph fastball with 1500 rpm, the drag (since it is thrown over 50 mph) would cause the ball to travel to home plate (60 ft away from the pitching rubber) in 1/2 a second slower than a non-spinning ball.

Physics Fun Fact of the Day - May 15

The mass of our entire atmosphere is estimated to be some 5.5 quadrillion tons.

Physics Fun Fact of the Day - May 14

The effect of Relativity made Astronaut Sergei Avdeyev a fraction of a second younger upon his return to Earth after 747 days in space.

Physics Fun Fact of the Day - May 13

The faster you move, the heavier you get.

According to the theory of relativity, mass and energy are equivalent. So therefore, the more energy you use, the more mass you gain.

Basketball - Starting, Stopping, and Changing Direction

A players' shoes must have good traction, which is the same as saying that the coefficient of friction between the shoe and the floor must be high. Friction is the force that opposes the motion of two surfaces that are in contact. Every surface is rough, on the microscopic scale, and when two surfaces come in contact, the high points on each surface temporarily make contact. The opposing or attracting forces of the surface molecules cause a 'frictional' force. A basketball player will also make use of static friction; a foot firmly planted, rather than slipping across the floor, will provide more friction when he has to stop or turn suddenly. This is because static friction ('pushing off') is greater than sliding friction ('sliding'). It is also why shoes must have a good grip on the floor in any direction you push off from, and why some shoes are unsuitable for basketball ... they may have lots of forward traction, but slip too easily when pushing sideways. It's just like driving ... spinning tires have less frictional force than non-spinning ones. ABS systems keep the tires from sliding, and maintain more friction.

Physics Fun Fact of the Day - May 12

According to the laws of gravity, the moon technically does not orbit the Earth. The two bodies actually both orbit around their common centre of gravity, which is located 1,000 miles beneath the surface of the Earth and is on a straight line between the centres of the Earth and moon. The centre of the Earth makes a small circle around that centre of gravity every 27 ¹/₃ days.

Physics Fun Fact of the Day - May 11

A car travelling at 80 km/h uses half its fuel to overcome wind resistance.

Basketball - Hang Time

Pro basketball players seem to float in the air while they're at the basket with the ball. Of course, this is just an illusion; they fall at the same rate as they rose into the air, assuming they don't make contact with anything. What makes the time seem longer is probably because after their bodies reach their highest point, they extend their arms upward, giving the illusion that they're still going up. They are also moving forward when they jump, which also affects our perception of time. Here's an example. Imagine firing a bullet from a rifle, directly at a monkey hanging from the branch of a tree a kilometre away. If the monkey lets go of the branch just as you fire, will you hit him? Leaving aside the environmentally sensitive issue of whether or not we should be shooting monkeys out of trees, this is actually a well-known physics problem. In fact, the moment the bullet leaves your gun in a horizontal line, it will begin to fall. It will fall with exactly the same acceleration downwards as the monkey. Regardless of how far away the monkey is, when the bullet reaches the tree, it will have fallen the same distance as the monkey. It will hit him!This seems unlikely, since we usually visualize bullets as travelling in a straight line. But as any hunter will tell you, they do fall. If aimed horizontally, the bullet will hit the ground in the same time another bullet would, if you dropped it from the same height as your gun.The 'hang time' of a pro basketball player at the net seems longer because he is moving forwards and upwards. It is harder to consciously be aware of how long it took him to go up, when he is also moving forwards. But if you used a stopwatch and a slow-motion replay, you would discover that the time from when he left the floor to when he stops moving upward is exactly equal to the time he takes to fall, and there is no hang time! The instant he stops going up, he starts to fall. But this is hard to see when things happen fast and there is forward movement.

Physics Fun Fact of the Day - May 10

A particle here can affect one on the other side of the universe, instantaneously.

"When an electron meets its antimatter twin, a positron, the two are annihilated in a tiny flash of energy. Two photons fly away from the blast.

Subatomic particles like photons and quarks have a quality known as “spin”. It’s not that they’re really spinning – it’s not clear that would even mean anything at that level – but they behave as if they do. When two are created simultaneously the direction of their spin has to cancel each other out: one doing the opposite of the other.

Due to the unpredictability of quantum behaviour, it is impossible to say in advance which will go “anticlockwise” and the other “clockwise”. More than that, until the spin of one is observed, they are both doing both.

It gets weirder, however. When you do observe one, it will suddenly be going clockwise or anticlockwise. And whichever way it is going, its twin will start spinning the other way, instantly, even if it is on the other side of the universe. This has actually been shown to happen in experiment (albeit on the other side of a laboratory, not a universe)."

Source: http://www.telegraph.co.uk/science/6546462/The-10-weirdest-physics-facts-from-relativity-to-quantum-physics.html

Baseball - The Curveball

"Balls curve as a consequence of asymmetries in the resistance of the air through which they pass." Which way it will curve all depends on this. If the resistance is stronger on one side, it will curve in the opposite direction. Because of a pitcher's release point, the way the ball curves all depends on one thing: which hand they are throwing the ball with. A right-handed pitcher throws the ball with more resistance coming from the third-base side and therefore would curve towards the first-base side. For a left-handed pitcher, it does the complete opposite. What is interesting about a curveball is that when the ball is thrown, from its initial point to its end point, the radius of the curve is almost always constant, making it actually curve perfectly (geometrically).

Physics Fun Fact of the Day - May 9

The fundamental description of the universe does not account for a past, present or future.

In the theory of relativity, Einstein states that there is no such thing as a past, present, or future (believe it or not). Time frames are relative, but since we are all moving at the same speed, ours are similar.

Physics Fun Fact of the Day - May 8

Black holes aren’t black.

If you look at a black hole closely, you will notice that they are dark, but you will also notice that there is a little light radiating from it, giving them color.

Physics Fun Fact of the Day - May 7

There are an infinite number of mes writing this, and an infinite number of yous reading it.

"According to the current standard model of cosmology, the observable universe – containing all the billions of galaxies and trillions upon trillions of stars mentioned above – is just one of an infinite number of universes existing side-by-side, like soap bubbles in a foam.

Because they are infinite, every possible history must have played out. But more than that, the number of possible histories is finite, because there have been a finite number of events with a finite number of outcomes. The number is huge, but it is finite. So this exact event, where this author writes these words and you read them, must have happened an infinite number of times.

Even more amazingly, we can work out how far away our nearest doppelganger is. It is, to put it mildly, a large distance: 10 to the power of 10 to the power of 28 meters. That number, in case you were wondering, is one followed by 10 billion billion billion zeroes."

Source: http://www.telegraph.co.uk/science/6546462/The-10-weirdest-physics-facts-from-relativity-to-quantum-physics.html

Basketball - Free Throws

For a player of given height, the exact force and direction necessary to give the ball a velocity that will result in a basket can be calculated exactly. There are no complications. The difficulty is that these quantities can't be measured exactly by eye, and the application of the force is through muscles which can't be controlled perfectly one hundred percent of the time. So in this case, physics won't help at all!So how does a professional basketball player manage to make so many shots successfully? The answer is 'kinesthetic memory' again. A player cannot possibly calculate the correct angle and force for a shot, and even if he knew what they were, couldn't reliably make his muscles do exactly what was necessary. Instead, the player practices the shot over and over, thousands of times. Golfers do this ... a pro golfer must hit tens of thousands of shots, practicing hours every day, year after year, before there is any hope that he will be good enough to play in the pro leagues. What the repetition does is familiarize the athlete with what a good shot feels like, and what movements he was making to achieve that perfect shot. It's the same in all pro sports.In the case of a pro basketball player, he makes the shot nearly every time because he 'lets his muscles do it' ... he does it exactly the same way he's done it thousands of times before, and doesn't have to think about it.

Physics Fun Fact of the Day - May 6

Things can travel faster than light; and light doesn’t always travel very fast.

The speed of light depends on the medium in which it is located, so light can travel relatively slow, allowing different objects to travel faster than them.

Physics Fun Fact of the Day - May 5

Events in the future can affect what happened in the past.

No, this is not Back to the Future or even some weird David Lynch film:

"According to an experiment proposed by the physicist John Wheeler in 1978 and carried out by researchers in 2007, observing a particle now can change what happened to another one – in the past.

According to the double slit experiment, if you observe which of two slits light passes through, you force it to behave like a particle. If you don’t, and observe where it lands on a screen behind the slits, it behaves like a wave.

But if you wait for it to pass through the slit, and then observe which way it came through, it will retroactively force it to have passed through one or the other. In other words, causality is working backwards: the present is affecting the past.

Of course in the lab this only has an effect over indescribably tiny fractions of a second. But Wheeler suggested that light from distant stars that has bent around a gravitational well in between could be observed in the same way: which could mean that observing something now and changing what happened thousands, or even millions, of years in the past."

Source: http://www.telegraph.co.uk/science/6546462/The-10-weirdest-physics-facts-from-relativity-to-quantum-physics.html

Physics Fun Fact of the Day - May 4

All the matter that makes up the human race could fit in a sugar cube.

Atoms are 99.9999999999999 per cent empty space. If you get rid of all the empty space, it would be more than easy to fit everyone into one small sugar cube. You would even have a lot of empty space!

Physics Fun Fact of the Day - May 3

If the Sun were made of bananas (or anything else for that matter), it would be just as hot.

It is hot because of its incredible weight, what it's made of does not matter.

Basketball - Layups

A good layup happens when the player does not take a shot, but uses the speed of his body to put him near the net. He just has to drop the ball in! (O.K., maybe slam it in.) The point is that it would be very difficult to shoot while you are also moving forward. Good players can make passes this way ... throwing while they are in the air, moving forward, and twisting around. But shooting at the basket, which is a much smaller target and at a different distance each time you do it, would be a hard shot to make while you're moving towards the net. (The ball's velocity would be the sum of your speed and the ball's) .Players always stop to shoot, to allow 'muscle memory' to do the shooting for them. Rather than practice this difficult skill, throwing from farther away while moving towards the net, players master the skill of the layup. They move their whole body through the air, protecting the ball as long as possible, and put it in the net when they're so close they can't miss.

Physics Fun Fact of the Day - May 2

A lightning bolt is 3 times hotter than the sun.

Physics Fun Fact of the Day - May 1

If you yelled for 8 years, 7 months and 6 days, you would have produced just enough sound energy to heat up one cup of coffee.

Baseball - Hitting

When a batter stands at home plate, ready to strike the ball with a bat, it is called hitting. There are many instances of physics in this process. One of these instances is in the action of swinging the bat. The average baseball player will take 150 milliseconds to start and finish his swing. At its peak, a player can swing the bat with a speed of 70 mph, faster than most speed limits on a freeway. To achieve this, a player puts most of his weight (let's say 180 lbs, the size of an average American) on his back foot. When he releases the energy now contained in his back foot, he releases a force of over 250 pounds in this 150 milliseconds. As he rotates his hips and brings his hands (and the bat) through, he uses the 250 pound force and the new 50 pound force created by his hands and the bat to strike the ball, a transfer of energy that takes less than a tenth of a second. However, the ball does not take all of the energy used by the batter. At most, it will take 1/2 the kinetic energy of the forces centered on the bat, and that is only if it is hit squarely. The ball will usually only take about 1/5 of the kinetic energy of the bat.