Physics Fun Fact of the Day - June 1

Physics is Fun :)

Light has weight. The weight of sunlight on the earth's surface has been determined to be two pounds per square mile.

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.