Energy transfers is the conversion of one form of energy into another, or the movement of energy from one form to another. Throughout this project, you will learn key terms about energy and energy transfers as well as the step by step energy transfers of when a soccer ball is kicked.

Momentum

When a soccer player kicks a ball, they transfers his momentum to the ball. Momentum is the velocity of object times its mass. Also when players pass the ball to each other, they use their feet to slow the momentum of the ball by moving with the ball and resisting it slowly. This way, they can have more control over the ball.

Analyzing a Kick

To analyze the kick we can treat it as an inelastic collision in one dimension, between the soccer ball and foot.

e=Vb2 - Vf2/Vf1 - Vb1

e =

coefficient of restitution which will always be zero or one. Zero meaning the colliding bodies stick together and move with the same velocity and one meaning the collision is elastic and kinetic energy is conserved.

Vb1 =

the velocity of the soccer ball before being kicked

Vf1 =

is the velocity of the foot before the kick

Vb2 =

the velocity of the soccer ball after the kick

Vf2 =

the velocity of the foot after the kick

Magnus Effect

The curve of the ball during flight is known as the Magnus Effect. As the ball spins, friction between the ball and air causes the air to react to the direction of spin of the ball. As the ball undergoes top-spin, it causes the velocity of the air around the top half of the ball to become less than the air velocity around the bottom half of the ball. The tangential velocity of the ball in the top half acts in the opposite direction to the airflow, and the tangential velocity of the ball in the bottom half acts in the same direction as the airflow. Therefore, when a soccer player kicks the ball right of center the ball spins counter-clockwise and the Magnus force acts left, causing the ball to curve left. When the ball is kicked left of center the ball spins clockwise and the Magnus force acts right, causing the ball to curve right.

Energy Transfers

Step by Step Energy Transfers

Definitions of Terms used Throughout this Project

**The Physics of Kicking a Soccer Ball**

1. In every action we make, chemical potential energy is available to do work because of nutrients in our bloodstream from the food that we consume. Thus forming energy for the kicker to perform the kick.

2. As the leg swings and builds up energy, potential energy is formed because it has the potential to do work

3. Once the ball comes in contact with the player's foot, the product of this reaction is sound energy. When someone kicks a ball, you can hear a very low pitched sound as the cleat collides with the ball making that sound travel through the air and vibrating materials into your ear. Also, once the force has been applied to the ball and creates motion, the potential energy changes to kinetic energy due to the position of the ball changing

4. After the kick, potential gravitational energy is present for the time the ball is kicked into the air. This is transformed to potential gravitational energy because the energy stored in the ball is based on its height and mass. As the ball’s height increases, the gravitational potential energy increases.

5. As the ball hits the ground, once again, sound energy is formed because of the impact between the ball and the ground creating more sound waves that our ears pick up

6. Most of the energy transfers after the ball lands on the ground transfers into thermal energy where the friction from the grass on the ball, slows the ball to a stop (friction transforms into thermal energy).

Potential Energy:

Stored energy in an object of its position or its configuration

Kinetic Energy:

The energy in which a body possesses because of its motion

Potential Gravitational Energy:

Energy changes into kinetic energy

Thermal Energy:

Due to the motion of particles, with motion being the key, also can be transferred from one object or system to another in the form of heat

Sound Energy:

The movement of energy through substances in longitudinal waves.

Tangential Velocity:

The linear speed of something moving along a circular path

Inelastic Collision:

Part of the kinetic energy is changed to some other form of energy in the collision.

As the ball moves through the air, the air resists the motion of the ball and the resistance force is called drag. Drag is directed along and opposed to the flight direction. In general, there are many factors that affect the magnitude of the drag force including the shape and size of the object, the square of the velocity of the object, and conditions of the air; particularly, the density of the air. Determining the magnitude of the drag force is difficult because it depends on the details of how the flow interacts with the surface of the object. For a soccer ball, this is particularly difficult because stitches are used to hold the ball together. So the surface of the ball is not smooth.To determine the magnitude of the drag, aerodynamics normally use a wind tunnel to measure the drag on a model. For a soccer ball, the drag can be determined experimentally by throwing the ball at a measured speed and accurately measuring the change in velocity as the ball passes between two points of known distance.

Rotational Energy

Potential Energy

PE = mgh

PE

= Energy (in Joules)

m

= Mass (in Kilograms)

g

= Gravitational acceleration of the earth (9.8 m/s^2)

h

= Height above earths surface (in meters)

Potential energy is the stored energy an object has because of its position or state

The standard unit for measuring potential energy is the joule, which is abbreviated as "J."

Kinetic energy waiting to happen

Potential Gravitational Energy

One type of potential energy comes from the Earth's gravity which is gravitational potential energy. Gravitational potential energy is the energy stored in an object based on its height and mass. To calculate the gravitational potential energy we use the following equation:

GPE = m*g*h

g = the standard acceleration of gravity which equals 9.8 m/s2.

h = determined based on the height the object could potentially fall. The height may be the distance above the ground or perhaps the lab table we are working on.

m = the mass of the object

Kinetic Energy

The energy an object has due to its motion

As long as an object is moving at the same velocity, it will maintain the same kinetic energy. To find kinetic energy:

KE = ½ * m * v2

m

= mass

v

= velocity

Kinetic energy is due to an object's motion while potential energy is due to an object's position or state

The kinetic energy produced because of the rotation of an object. Rotational energy occurs when any form of matter rotates around a center of rotation. Rotational energy can be transformed into other forms of energy, particularly heat and translational energy due to friction.

Erotational = 1/2 I ω ^ 2

ω = angular speed,

I = the moment of inertia around the axis of rotation

E = kinetic energy

The mechanical work needed for or which is applied throughout rotation is the torque (a twisting force) times the rotation angle. The immediate power of an angular accelerating body is the torque or twisting force times the angular frequency.

How Potential Energy changes into Kinetic Energy

An object has potential energy (stored energy) when it is not in motion. Once a force has been applied or it begins to move, the potential energy changes to kinetic energy (energy of motion).

Energy and Momentum

Elastic Collision:

An encounter between two objects in which the total kinetic energy of the two objects after the encounter is equal to their total kinetic energy before the encounter.

Conserved low energy collisions between atoms, molecules, subatomic particles

Momentum is conserved and there is no loss of kinetic energy in the collision

Inelastic Collision:

Part of the kinetic energy is changed to some other form of energy in the collision

Both kinetic energy and momentum are conserved

For Kicking a Ball:

It would be considered as perfectly elastic which means the momentum is conserved

a collision between objects during which there is no loss of kinetic energy and energy is fully conserved