To investigate the factors that affect the height at which a ball bounces.

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Aim: To investigate the factors that affect the height at which a ball bounces.

Background Information:

Energy can neither be created or destroyed. It can only be converted from one form to others. The total amount of energy in any isolated system remains constant.

Types of Energy

  • Kinetic

Kinetic energy is the energy a body has by virtue of its motion. The amount of Kinetic energy an object has can be calculated using the following equation:

Kinetic Energy = ½ x Mass x Velocity

KE = ½ m v

J = ½ x Kg m/s 

  • Thermal

Thermal (or Heat) energy is also measured in Jules. It is energy that an object possesses because it is hot. Thermal energy will conduct or convect from a hot object or area, into a colder object or area. This causes heat to dissipate.

  • Gravitational Potential

Potential energy is stored energy that depends upon the relative position of various parts of a system. The work that gravity can do to an object (if it should fall) is called gravitational potential energy. The equation to work out the amount of gravitational potential energy an object has is as follows:

Gravitational P.E = mass x acceleration due to gravity x height

G.P.E = m g h

J = Kg x m/s x metres

Gravitational potential energy is directly proportional to the height of the object. Therefore, if the object was twice as high, it would have twice as much gravitational potential energy. How the object was raised to its height is irrelevant, gravitational potential energy is independent of the path that particles travel, the object will always have gravitational  potential energy.

  • Elastic Potential

Concept of Elasticity

ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed. A body with this ability is said to behave (or respond) elastically. Rubber-like materials and other polymers consist of long-chain molecules that uncoil as the material is extended and recoil in elastic recovery. the elastic response of any solid in tension can be characterized by means of a stored-energy function. Strain energy is the energy stored in an object when it is stretched, also known as elastic potential energy, when the object is allowed to return to its normal shape the energy is released.

How Energy is Transferred as a ball falls.

In ideal conditions. When the ball of mass 0.02kg is 1m above the ground, it has“200g x 10m/s x 1m”(2000 J) gravitational potential energy. As it falls, this energy becomes kinetic energy. And when it has fallen half-way to the ground (50cm) it has 1000 J kinetic energy and 1000 J gravitational potential energy. Just before the ball impacts the ground, it has 2000 J kinetic energy. On impact this becomes elastic potential energy. And this becomes kinetic energy as the ball bounces.  However, much energy is lost as heat, through friction with the air, and sound when the ball impacts. And as the ball bounces vertically, it is being pulled back down by gravity.

Why an object (e.g. a ball) bounces

The ball collides with a surface.  Kinetic energy in the particles at the rear of the ball keeps them moving forward, causing the ball to compress (“squash”) against the wall. Elasticity in the ball causes the ball to expand to its original shape, this expansion pushes the ball off the surface.

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Why a sphere bounces better than a cube

When a sphere bounces, the force is concentrated in a single point on the sphere, a surface small area, this results in high pressure. And because there is more pressure, there is more compression, and so, more expansion. While, in a cube, the force will be evenly distributed across a large surface area, resulting in low pressure. And because the force is evenly distributed, there is less compression, and so less expansion. This is why a cube (or any other flat-faced object) does not bounce as well as a sphere. And ...

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