Help With Bouncing Projectiles in Physics

How Projectiles Are Launched.

• The motion of a projectile can be described in terms of its changes in energy. Before its launch a projectile has zero kinetic energy. Energy is imparted to the projectile either by an explosion of chemical energy in a gun or cannon, from the energy of an extended bow with a bow and arrow or simply by the action of throwing a football or baseball. Dropping a projectile vertically is the simplest example of external propulsion, as the force of gravity causes the projectile to accelerate toward the ground.

Projectile Motion and Energy Transfer.

• At launch a projectile has maximum kinetic energy and will start to slow as it gains height. At peak height it has maximum potential energy, which is then transferred to kinetic energy as the projectile falls to earth. When it collides with the ground the projectile loses some or all of its energy in the form of heat. The projectile bounces and will continue to move until all of the energy has been dissipated.

Elastic and Inelastic Collision.

• The extent to which a particle will bounce depends on the elasticity of its collision with the ground. A completely inelastic collision is one where all of the energy is transferred from the projectile to the ground. A very soft or adhesive projectile will experience this type of collision and produce no bouncing. A projectile undergoing a completely elastic collision with the ground would bounce at the same height indefinitely. In practice, there is no such thing as a completely elastic collision, as any contact with the ground features a loss of energy, either through heat or sound.

Forces Acting on a Bouncing Projectile.

• A vertically bouncing projectile is subject to three forces. The first is the gravitational force between the projectile and Earth, always a vertically downward movement. The second force is due to the impact between the projectile and the ground. The elasticity of this impact dictates how high the projectile will bounce and therefore how many times it will bounce. The final force is air resistance, a frictional force that opposes the projectile's motion in both directions. Air resistance slows both the downward acceleration due to gravity and the upward motion of the projectile following impact with the ground.