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Physics > Conservation And Dissipation Of Energy > Flashcards

Conservation And Dissipation Of Energy Flashcards

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1
Q

What are the ways energy can be stored?

A 
Chemical 
Kinetic 
Gravitational potential energy 
Elastic potential energy 
Thermal energy stores
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2
Q

What chemical energy?

A

These stores include fuels, foods, or chemicals found in batteries The energy is transferred during chemical reactions.

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3
Q

What is a kinetic store?

A

The energy an object has because it is moving.

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4
Q

What is a gravitational potential store?

A

The energy stored in an objects because of its position

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5
Q

What is an elastic potential store?

A

The energy stored in a springy object when you stretch or squash it.

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6
Q

What is a thermal energy store?

A

The energy a substance has because of its temperature.

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7
Q

What is a closed system?

A

Where no resistance acts upon the object. For example, a vacuum.
The total energy is the same before and after energy transfers to the other energy stores within the closed system.

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8
Q

What is the conservation of energy?

A

Energy cannot he created or destroyed.

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9
Q

When is work done on an object?

A

When an object is moved by a force. This force transfers energy to the object.
Therefore, the amount of energy transferred to the object is equal to the work done on it.

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10
Q

What is energy transferred equal to?

A

Energy transferred = Work done

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11
Q

Work done to overcome friction is mainly transferred to what energy store?

A

Thermal energy store by heating.

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12
Q

When you rub your hands together they become warm. Why?

A

Your muscles do the work to overcome the friction between your hands. The work you do is transferred as energy that warms your hands.

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13
Q

What is the force you need to lift an object at a constant velocity equal and opposite of?

A

The gravitational force on the object.

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14
Q

What happens when an object is moved upwards?

A

The energy in its gravitational potential energy store increases. This increase is equal to the work done on it by the lifting force to overcome the gravitational force on the object.

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15
Q

What does the work done on an object moving up or down depend on?

A

How far it is moved vertically - it’s change in height.

It’s weight.

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16
Q

What is the weight of an object in Newton’s equal to?

A

Mass x Gravitational Potential Field Strength.

17
Q

What is useful energy?

A

Energy transferred to where it is wanted in the way that is wanted.

18
Q

What is wasted energy?

A

The energy that is not usefully transferred.

19
Q

Does friction cause energy to be wasted?

A

Yes.

20
Q

What happens to the energy when you are exercising.

A

When you exercise, energy is transferred to the thermal energy store of your muscles (so you get hot) and to the thermal energy store of the machine by the force you exert to overcome the friction in the machine.

21
Q

What energy is wasted from an electric heater?

A

Light emitted from the glowing element.

22
Q

How do clockwork radios work?

A

You turn a handle which winds up a spring. When the spring unwinds, energy from its elastic potential energy store is transferred to its kinetic energy store and it turns a small electric generator in the radio. Therefore, it doesn’t need batteries or mains electricity.

23
Q

What is power?

A

The rate of energy transfer.

24
Q

What happens when energy spreads out?

A

Energy becomes less useful the more it spreads out. Useful energy will eventually spread out.

25
Q

Why do devices waste energy?

A

Friction between the moving parts causes heating
The resistance in a wire causes the wire to get hit when current passes through it
Air resistance
Sound created

26
Q

How can you reduce the amount of energy wasted?

A

Lubricate the moving parts to reduce friction.
Use wires with little resistance.
Streamline the objects to reduce air resistance.
Cut out noise e.g. tighten lose parts to reduce vibration.

27
Q

What is the total power in?

A

The energy per second supplied to it.

28
Q

What is the useful power out?

A

The useful energy per second transferred to it.

29
Q

What is the equation for work done?

A

work done = force applied x distance moved along the action of the force

30
Q

How do you calculate the change in an object’s gravitational potential energy store?

A

change in object’s gravitational potential energy store = weight x change in height.

31
Q

How do you calculate an object’s gravitational potential store?

A

gravitational potential = mass x gravitational field strength x change of height.

32
Q

How do you calculate kinetic energy?

A

kinetic energy = 0.5 x mass x velocity*2

33
Q

How do you calculate elastic potential energy?

A

elastic potential energy = 0.5 x spring constant x extension*2.

34
Q

How do you calculate the efficiency of an object?

A

efficiency = useful output energy transferred by the device (J)/total input energy supplied by the device (J).

35
Q

How can efficiency be improved?

A

lubricate the moving parts to reduce friction
use wires with as little electrical resistance as possible
streamline the shapes of moving objects to reduce air resistance.
cut out noise (eg tighten lose parts to reduce vibration).

36
Q

What does it mean if an object is more powerful?

A

The more powerful an appliance is, the faster the rate at which it transfers energy.

37
Q

What is the equation for power?

A

power = energy transferred to appliance / time taken for energy to be transferred.

38
Q

How do you calculate wasted power?

A

power wasted = total power in - useful power out.

39
Q

How do you calculate the efficiency (power)?

A

efficiency = (useful power out/total power in) x 100.

Physics (25 decks)

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