Chapter 1: Conservation and dissipation of energy Flashcards
1
Q
Changes in energy stores
A
- Energy can be stored in different stores
- Energy is transferred, by waves, electric circuit, or by a force when it moves an object.
• When an object falls and gains speed, its gravitational potential energy store decreases and kinetic energy store increases
`
• When a object hits the floor, it kinetic energy store decreases and the energy it transferred into the thermal energy store, by sound waves.
2
Q
Conservation of energy
A
- Energy can not be created or destroyed
- Applies to all energy changes
- A closed system is when no energy is transferred in or out of the energy stores in the system
- Energy can be transferred between stores in a closed system. The total energy is the same before and after and transfers in the system
3
Q
Energy and work
A
- Work is done on an object when a force makes the object move
- Energy transferred = work done
- Work done is work done, W = force, F x distance object, s has moved
- Word done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and to the surroundings
4
Q
Gravitational potential energy stores
A
- It increases when an object moves up and vice versa
- The gravitational potential energy increases when an object is lifted up because work was done to lift the object up against gravity
- Gravitational potential energy, ΔE = mass, m x gravity, g x height, Δh
5
Q
Kinetic energy and elastic energy stores
A
- Kinetic energy store of a moving object depends on its mass and its speed
- Kinetic energy, Ke = ½ x mass, m x velocity2, v
- Elastic potential is the energy stored on an elastic object when work is done on it
- Elastic potential energy, Ee = ½ x spring constant, k x extension2, e
6
Q
Energy Dissipation
A
- Useful energy is energy in the place we want it and in the form we need
- Wasted energy is the energy which is not useful and is transferred in an undesired way
- Wasted energy will eventually be transferred into the surroundings which will become warmer
- As energy dissipates it gets less and less useful
7
Q
Energy and efficiency
A
- Efficiency = useful energy / total energy
- Machines waste energy through: friction of moving parts, noise, air resistance, electrical resistance
- Machines can be more efficient by making them waste less energy; for example: lubricating moving parts reduces friction so less thermal energy is surrounded into the surroundings, wasted.
8
Q
Electrical Appliances
A
- Electricity and gas or oil supply most of the energy you use in your home
- They transfer useful energy when you turn them on
- Examples: heating, lighting, making objects move
- Designed for a purpose and should be as efficient as possible
9
Q
Energy and power
A
- Power is the rate of energy transferred
- Power, P = energy, E x time taken, t
- Power wasted = total power in – useful power out
