Projectile Motion Lab Experiment and Report

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Introduction

Projectile motion exists commonly in our everyday lives and is evident in the motion or flight of objects which are projected in the air at angles. Examples of projectiles range from a golf ball in flight, to a curve ball thrown by a baseball pitcher to a rocket fired into space. A projectiles pre-determined path of flight (parabola) is influenced by a number of factors including:

1. The force applied
2. The angle of release
3. The height of release
4. Once a projectile is released into the air it is automatically under the influence of gravity and air resistance.

Air resistance is a force working against motion. Gravity acts against motion by pulling the object back towards the ground. This occurs in many different sports, more so the one that use a ball however gravity and air or water resistance is present in every sport.

Aim

To demonstrate the interrelationship between the angle, height and velocity of release on the flight path and distance of a projectile.

Hypothesis

There is a relationship between a projectiles distance of flight and its flight path and the amount of force applied to the projectile, the angle of release of the projectile and the height at which the projectile is released.

Prediction

The closer to the optimal height, angle and force of release applied to a projectile the further it will go.

Materials

• Medicine balls
• Chair
• Measuring tape
• Markers

Procedure

The ball was thrown in two hands from standing on the ground, standing on a chair and kneeling on the ground. Each test was done three times and the results were measured and recorded. The thrower then took a five step run up and threw the ball, this was done three time and the results were measured and recorded. The ball was then thrown parallel to the ground, at a forty-five degree angle and a seventy degree angle, the ball was thrown three times at each angle and the results were measured and recorded.
Results:

Table 1: Show the relationship between the angle, height and velocity of release on the flight path and distance of a projectile.

Discussion

The height of release in which the ball travelled the furthest distance was the one standing on the chair. The average for a ball being thrown by a person standing on a chair was 6.78 metres, which was the second greatest distant out of all the tests. This is related to the prediction as the higher the height of release the further a projectile should travel. This however is only if you take the height of release into consideration, and not the presence of air resistance and gravity. This was predicted as standing on the chair is the closest to optimal height of release out of the three tests done on height of release.

The angle of release at which the ball travelled the furthest was 45 degrees. The average for a ball being thrown at a 45 degree angle was 6.05 metres, which was the third greatest distance. This agrees to the previously made prediction, stating that the optimal height of release would be 45 degrees, and that the optimal height of release would travel the greatest distance. Even though the angle at which the ball was thrown would not have been exactly 45 degrees it would have been much closer than the throws done at parallel and 70 degrees with the ground.

The run up affected the range through its summation of force. This is so as there were more body parts in motion, and momentum was being built up whilst taking the run up. The results prove this as the ball thrown from a run up recorded the greatest distance at 8.63 metres. This agrees with the prediction as there was maximal forced applied to the ball after a five step run up resulting in making it go as far as possible.

Based on the results that have been obtained, it is recommended that when throwing a ball it should be thrown at a 45 degree angle, after a run up while standing on a platform raised above the ground. This would be the common recommendation when throwing a ball, in order to get maximum distance. However in the sport that is related to the unit that has been studied, (which is cricket) the ball would have to be bowled at different angles, force, and height in order to get the best results for the type of bowl that the bowler is trying to do. For example a pace bowler would have a faster and longer run up then a spin bowler in order to get more pace on the ball. As would a spin bowler have to release the ball at a different height (bend over more) and angle in order to get the type of spin that they want.

Five sport in which a coach can use this knowledge to improve their trainee’s performance are:

Javelin

Javelin probably relates to this more than most trowing sports because it involves a much bigger run up. When a javelin is thrown the angle of release is probably at a higher angle that the usual 45 degree release. This has got to do with the weight and shape of the projectile being thrown, (long and thin).

Boomerang throw

Throwing a boomerang involves different angles, force and height of release than normal projectiles. This is because they are designed to return to the thrower after being released. A boomerang is usually thrown at around a 70 degree angle.

Shot put

As shot puts are similarly proportioned in size and shape, and weigh the same as the balls being thrown in the original tests done, the dimensions used in the propelling of a shot put would be ones similar to the results.

Discuss throw

When throwing a discuss, rather than running up to build momentum an athlete will spin around in a circle and swing their arm, in order to get maximum distance/performance. This is again because of the shape of the projectile, it being a disc not a ball.

Hammer throw

The hammer throw involves a similar build-up of momentum to the discus throw. However instead of it being a disc held in one hand it is a ball (the same as a shot put) attached to a chain, held in both hands. Having the same angle of release as the discus at about 60 degrees.

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