GSCE Physics: P1 Conservation and Dissipation of Energy

Different types of energy stores

• Gravitational Potential Energy

• Kinetic Energy

• Thermal Energy

• Chemical Energy

• Elastic Potential Energy

What is the conservation of energy?

The conservation of energy is that energy cannot be created or destroyed, only transferred from one form to another.

What energy transfers happen when bungee jumping?

Gravitational potential energy is converted to kinetic energy as the jumper falls. Kinetic energy is then transferred to elastic potential energy as the bungee cord stretches. Finally, the elastic potential energy is converted back to kinetic energy as the jumper rebounds upward.

What is the equation for work done?

Force applied x Distance

What is work done transferred into to overcome friction?

Thermal energy

What is the equation for gravitational potential energy store of the change in an object?

Weight x Change of height

Equation for Gravitational Potential Energy

Mass x Gravitational Field Strength x Change of Height

Equation for Kinetic energy

½ x Mass x velocity²

Equation for elastic potential energy

½ x spring constant x extension²

What is hooke’s law?

The extension of a spring is proportional to the force applied within the elastic limit

What is useful energy and wasted energy?

Useful energy - energy transferred to where it is wanted the way it is wanted

Wasted energy - energy that is not fully transferred

What is dissipation?

When the energy that is not fully transferred (wasted energy) spreads out and can be stored in less useful ways

Why is there always wasted energy in machinery?

Friction is always the cause to wasted energy in machines e.g when using a drill, the friction causes heat which is wasted

Equation for efficiency

Useful output energy / Total input energy

Friction, the resistance of a wire, air resistance and sound are all causes of wasted energy in machinery. Describe a way to reduce the wasted energy for each one

Friction - using lubricants, reducing friction

The resistance if a wire - use wires with less electrical resistance

Air resistance - streamlining the shapes of moving objects to reduce air resistance

Sound - tighten looser parts to cut out sound caused by vibration

What is the useful and wasted energy in a hairdryer?

Useful energy: Kinetic energy (air from fan) and energy heating air

Wasted energy: Sound energy and the hairdryer heating up

Equation for power

Energy transferred / Time

Equation for efficiency (including useful and total power input)

Useful power output / total power input x 100

Equation for wasted power

wasted power = total power input - useful power output

Equation for force

mass x acceleration