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P1 > .6 > Flashcards

.6 Flashcards

1
Q

Why is heat energy wasted in machines?

A

Because of the friction of the moving parts, causes the parts to warm up.

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2
Q

Useful energy

A

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

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3
Q

Wasted energy

A

Energy that is not usefully transferred

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4
Q

Input energy

A

Useful output energy + wasted energy

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5
Q

How to reduce wasted energy in moving oarts?

A

Lubricate the parts.

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6
Q

How to reduce wasted energy in wires?

A

In prder to stop the wire getting hot when a current passes through it, use wires with as little electrical resistance as possible.

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7
Q

How to stop wasted force to the surroundings by air resistance?

A

Streamline the shapes of moving objects.

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8
Q

How to stop wasted emergy in sound created by machinery?

A

Cut out noise, tighten loose parts to redcue vibration.

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9
Q

What three things supply your house with energy?

A

Electricity, gas, and oil.

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10
Q

What is the useful energy from the lightbulb

A

Light emitted from the glowing filament

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11
Q

What is the wasted energy from the lightbulb

A

Energy transferred from the filament heating the surroundings

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12
Q

What is the useful and wasted energy from an electric heater?

A

Useful: energy heating the surroundings
Wasted: light emitted from the glowing element

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13
Q

What is the useful and wasted energy from an electric toaster?

A

Useful: energy heating bread
Wasted: energy heating the toaster case and the air around it

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14
Q

What is the useful and the wasted energy from an electric kettle?

A

Energy heating the water is useful. Energy heating the kettle itself is not useful.

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15
Q

What is a useful and wasted energy from a hairdryer?

A

Kinetic energy of the air driven by the fan and energy heating flowing past the heater filament is useful. Sand and energy heating hairdryers is not useful.

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16
Q

What is the useful and wasted energy for an electric motor

A

Kinetic energy of the objects driven by the motor and gravitational potential energy of objects lifted by the motor is useful. Energy heating the motor and sound is not useful.

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17
Q

How does a clockwork radio work?

A

Basically you wind it up. You turn the handle and wind up a clockwork spring and increase the elastic potential energy of the spring and when this unwinds energy from his elastic potential energy stores transfer to its kinetic energy store and it turns a small electric generator in the radio.

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18
Q

Power wasted

A

Total power in - useful power out

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19
Q

What do good insulators have?

A

Low thermal conductivity, so energy transfer through them is as low as possible.

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20
Q

What does thermal conductivity depend on(3 things)?

A

One. The temperature difference across the material. Two. The thickness of the material. Three. The thermal conductivity of the material.

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21
Q

What are two ways to reduce energy transfer as much as possible in any given situation?

A

One. The thermal conductivity of the insulating material should be as low as possible. Two. The thickness of the insulating layer should be a thick as practically possible.

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22
Q

Why is fibreglass a good insulator

A

Because air gets trapped between the fibres and heats up

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23
Q

What three things does temperature rise depend on?

A

The amount of energy supplied, The mass of the substance and what the substance is

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24
Q

What is specific heat capacity?

A

The specific heat capacity of a substance is the energy needed to raise the temperature of 1 kg of the substance by 1°C.

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25
Q

What is the unit for specific heat capacity

A

J/kg°C

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26
Q

What is the storage heater?

A

It uses electricity at night to heat special bricks or concrete bricks in the heater. Energy transferred from the bricks keep the room warm. The bricks have a high specific heat capacity so they store lots of energy. They warm up slowly when the heater element is on and cool down slowly when it is off.

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27
Q

Waht are some methods to reduce home heating bills?

A

Loft insulation

Cavity wall insulation

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28
Q

How does the loft insulation save money?

A

Fiberglass traps air, which helps to reduce the rate of energy transfer by conduction.

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29
Q

How does cavity wall insulation help save money?

A

Insulation is pumped into the cavity between the two layers of brick. It is a better insulator than the air it replaces. It traps the air in small pockets.

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30
Q

How does aluminium foil between a radiator and a wall help save money?

A

It refelcts the radiation away from the wall so it reduces the rate of energy transfer by radiation.

31
Q

How do double -glazed windows help save money?

A

Dry air between two glass panes. The thicker the glass, the lower the themal conductivity. Dry air is a good insukator, somit reduces the rate of eenergy transfer by conduction and because it is a vacuum, this prevents the enrgy transfer by convection.

32
Q

How do thicker bricks help save money?

A

The rate of transfer of energy from the inside to the outside will be lower and the cost of heating will be less.

33
Q

Ways energy is transferred?

A

By heating, waves, an electric current or when a force moves an object.

34
Q

Different types of energy stores?

A 
Chemical energy stores
Kinetic energy stores
Gravitational potential energy stores
Elastic potential energy stores
Thermal energy stores
35
Q

Info on chemical energy stores

A

Include, fuels, foods, or chemicals in batteries. The energy is transferred during chemical reactions.

36
Q

Info on kinetic energy stores

A

The energy an object has because it is moving.

37
Q

Info on gravitational potential energy stores

A

Energy stored in an object because of its position.

38
Q

Info on elastic potential energy stores

A

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

39
Q

Info on thermal energy stores

A

Describes the energy a substance has because of its temperature.

40
Q

How does a torch work?

A

The torch’s battery pushes a current through the bulb. This makes the torch bulb emit light and also get hot.

41
Q

How does an electric kettle work?

A

The current in the kettle’s heating element transfers energy to the thermal energy store of the water and the kettle.

42
Q

Energy stores when an object is thrown into the air?

A

The object slows down as it goes up. The energy is transferred from the object’s kinetic energy store to the gravitational potential energy store

43
Q

Energy stires when an object falls freely?

A

It speeds up as it falls. The force of gravity acting on the object causes energy to be transferred from its gravitational potential energy store to its kinetic energy store.

44
Q

Changes in energy stores in a torch lamp?

A

Chemical energy store in the battery to the electric current in the wires and energy is transferred to the surroundings in light waves and an increase in the thermal energy store of the surroundings.

45
Q

Energy transfers when an object falls and hits the ground?

A

From the gravitational potential energy store to the kinetic energy store and energy is transferred to the surrounding, in the form of sound waves and an increase in the thermal energy store of the surroundings.

46
Q

Energy stores in a roller coaster?

A

As a roller coaster climbs an incline, its gravitational potential enrgy store increases. This energy then transferred to other energy stores as it races downwards. As the roller coaster descends, its gravitational potential energys tores decreases and most of this energy is transferred to its kinetic energy store, which increases. Some energy is transferred to the thermal energy store of the surroundings by air resistance and frictiona nd some energy transferred by sound waves.

47
Q

Describe energy transfers in a pendulum?

A

As it moves towards the middle, energy is transferred by the force of gravity from its gravitational potential energy store to its kinetic energy store. So its GPE store decreases and its kinetoc energys tire increases. As it moves away from the middle, its kinetic energy store decreases and its GPE store increases. If the air resistance on the bob is very small, the bob will reach the same height on each side.

48
Q

What is a system and rules of a system?

A

A system is an object or group of objects. The total energy of a closed system is always the same before and after energy tranfers to other energy stores within the closed system.

49
Q

Example of a closed system

A

If a pendulum was swinging in a vacuum, it may keep on swinging forever because there is no air resistance acting on it, so no energy would be transferred from any of its energy stores. There would be no net change to the energy stored in the system.

50
Q

What is the principle of conservation of energy?

A

Energy cannot be created or destroyed.

51
Q

Energy transfers in bungee jump (pre bounce)

A

When the rope is slack, energy is transferred from the GPE store to the kinetic energy store as the junoer accelerates towards the ground due to the force of gravity. When the rope tightens, it slows the jumper’s fall. This is because the force of the rooe reduces the speed of the jumper. The jumper’s kinetic energy store decreases and the rope’s elastic potential energy store increases as the rop stretches. The jumper comes to a stop and the energy that was originally in the kinetic energy store of the jumper, has all been transferred into the EPE store of the rope. After reaching the bottom, the rope recoils and pulls the jumper back.

52
Q

Energy transfers in bungee jump(bounce)

A

After the rope recoils and pulls the jumper back, and the jumper rises. The energy in the EPE store of the rope decreases and the bungee jumper’s kinetic energy store increases until the rope becomes slack. After it does, at the top of the ascent, the jumper’s K energy store decreases to zero. The bungee jumper’s GPE increases throughout the ascent. The jumper doesn’t return to original height, because some energu was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again.

53
Q

When an object is moved by a force…

A

Work is done on the object by the force. So the force transfers energy to the object. The amount of energy transferred to the object ks equal to the work done on it.

54
Q

Energy transferred=

A

Work done

55
Q

Equation for work done by a force when it causes displacement of an object?

A

Work done=force applied x distance moved

along the line of action of the force

56
Q

Work done to overcome friction is mainly transferred to….

A

Thermal energy stores by heating.

57
Q

Example of friction at work with hands

A

If you rub your hands togetherm they become warm. Your muscles do work to ivercome the friction between your hands, the work you do is transferred as energy that warms your hands.

58
Q

Friction at work in brakes

A

Brake lads on a vehicle become hot is brakes applied for too long, As friction between the brake pads and the wheel discs opposes the motion of the wheel. Kinetic energy store of vehicle to thermal energy store of brame pads and wheel disks and transfer this energy to surrounding air.

59
Q

Friction at work with meteorites

A

They pass through the atmosphere, but friction is caused by air resistance acts upon them. This results in energy being transferred from the meteorite’s GPE store and K store to the meteorite’s thermal energy store, causing it to heat up. If it becomes hot enough, glows.

60
Q

The surface of a space vehicle is designed to withstand ….

A

the very high temps caused by this friction when it re-enters Earth’s atmosphere.

61
Q

Energy transfers when you lift an object up?

A

Some of your muscles transfer energy from the chemical energy atore in the muscles to the gravitational energy store of the objects.

62
Q

The force you need to lift an object at constant velocity is equal and opposite to the…

A

gravitational force on the object. So the upward force you need to apply to it is equal to the object’s weight.

63
Q

The work done when an object moves up or down depends on:

A
  1. How far it is moved vertically (its change of height)

2. Its weight

64
Q

Equation for work done

A

Work done=force applied x distance moved in the direction of the force

65
Q

Equation for change in object’s gravitational potential energy store

A

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

66
Q

Why can astonauts on the moon lift objects much more easily than they can on Earth?

A

Because the gravitational field strength on the Moon’s surace is only about a sixth of the gravitational field strength on the Earth’s surface.

67
Q

Equation for change of GPE store?

A

Change of GPE store= mass x gravitational field strength x change of height

68
Q

The energy an object has because of its motion depends on its …

A

Mass and speed. This energy is called kinetic energy.

69
Q

Because the height drop is a measure of the ball’s kinetic energy store, it can be said that the ball’s kinetic energy store is …

A

directly proportional to the square of the speed.

70
Q

Equation for kinetic energy

A

Kinetic energy = 1/2 x mass x speed ^2

71
Q

Equation for elastic potential energy

A

EPE = 1/2 x spring constant (k) x extension ^2

72
Q

Hooke’s law equation

A

F=ke

73
Q

How energy wasted on a bike and while lifting weights?

A

Because it is transferred from kinetic energy stires of bike and cyclist to the thermal stores of the brake blocks and wheels, which are heated by friction.
Energy transferred to thermal energy store of your muscles.

P1 (6 decks)

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