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Physics GCSE > Section 4 - Forces and Energy > Flashcards

Section 4 - Forces and Energy Flashcards

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1
Q

What is a system?

A

A single or group of objects

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2
Q

What happenes when a system changes?

A

Energ is transferred

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3
Q

What is a closed system?

A

A system with no net change in energy

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4
Q

How can energy be transferred?

A

Heat
Force
Electricity

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5
Q

Describe the energy transfers that occur when the wind causes a windmall to spin?

A

The wind does work on the windmill causing it to turn and transferring energy to the kinetic energy store of the windmill

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6
Q

What is the work done equation?

A 
E = F x d
Energy = Force x Distance
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7
Q

What does 1 J equal?

A

1 Nm

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8
Q

What does a force doing work often result in?

A

A rise in temperature

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9
Q

What is power?

A

How much work is done per second (rate of energy transfer)

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10
Q

What is the equation for power?

A 
P = E / t
Power = Energy / Time
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11
Q

If an electric heater has a power of 600W and it is left on for 3 seconds, how much energy is transferred?

A 
P = E / t
E = P x t
E = 600 x 3
E = 1800 J
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12
Q

A motor does 4.8 kJ of work in 2 minutes

Find its power output?

A

4.8 kJ = 4800 J

P = E / t
P = 4800 / 120
P = 40 W
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13
Q

A constant force of 20 N pushes an object 20 cm

Calculate the work done

A 
E = F x d
E = 20 x 0.2
E = 4 J
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14
Q

An appliance transfers 6000 J of energy in 30 seconds

Calculate its power

A 
P = E / t
P = 6000 / 30
P = 200 W
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15
Q

What do interactions between objects cause?

A

Forces

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16
Q

What are interaction pairs?

A

A pair of forces that are equal but opposite

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17
Q

What does a free body force diagram show?

A

An object and all the forces acting on it

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18
Q

What should free body force diagrams include?

A

Every force acting on the body

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19
Q

What shouldn’t free body force diagrams include?

A

The forces the object exerts on the rest of the world

20
Q

What is the resultant force of an object in equilibrium?

A

Zero

21
Q

What happens to objects that have no resultant force?

A

They are either stationary or moving at a steady speed

22
Q

How do you draw a scale drawing

A

Set a scale
Draw the forces acting on an object from tip to tail (one at a time)
Then draw a line from the start to the end
Measure the length and the angle

23
Q

How do you resolve a component force?

A

Draw it on a scale grid and measure the horizontal and vertical vectors

24
Q

What must a bearing always be presented as?

A

A three digit number

25
Q

What is a moment?

A

The turning effect of a force

26
Q

How do you calculate the moment?

A 
M = F x d
Moment = Force x Distance
27
Q

In terms of moment, why is pushing at any other angle bad?

A

It means a small distance which means a smaller moment

28
Q

What is the principle of moments/

A

For an object in equilibrium

The sum of the clockwise moments = The sum of anticlockwise moments

29
Q

What do levers do?

A

Transfer the turning effect of a force

30
Q

How do levers make it easier to do work?

A

They increase the distance from the pivot at which a force is applied, therefore the smaller the force to give the same moment

31
Q

What are gears used to do

A

Transmit the rotational effect of a force from one place to another

32
Q

Describe the moment of a small gear with a force applied to it?

A

A small moment

33
Q

How do gears increase the moment?

A

If the next gear is larger, the force is applied further from its pivot, so the moment is larger

34
Q

How does the size of the gear affect its speed?

A

The larger the gear, the slower it spins

35
Q

How do you work out how the speeds and moments will change between gears ?

A

By looking at the gear ratios

36
Q

The largest gear has 16 teeth and the medium gear has 8

What is the ratio?

A

16 : 8
4 : 2
2 : 1

37
Q

If a larger gear and a smaller gear have a ratio of 2 : 1 what does this mean?

A

For every rotation of the larger gear the smaller gear has rotated twice

38
Q

A 10N force is applied normal to a door, 85 cm from its hinges
Calculate the moment created

A

85 cm = 0.85 m

M = F x d
M = 10 x 0.85
M = 8.5 Nm
39
Q

What is the unit for moment?

A

Nm

40
Q

What is the ratio of moments of two gears equal to?

A

The ratio of the gears radii

41
Q

If a gear has 5N applied to it, what is the force of a second gear that is directly connected it?

A

5N (the same)

42
Q

Describe how to convert between J and Nm?

A

Divide by 1 (do nothing)

43
Q

What force causes the repulsion of two like electrical charges?

A

Electrostatic forces of repulsion

44
Q

A parachuter has a weight of 900 N
At one point during his fall, the air resistance acting on him is 500 N
In what direction is his resultant force at this point?

A

Down at 400 N (900 - 500 = 400)

45
Q

If a gear is spinning clockwise, what direction will a second gear directly connected to it spin?

A

Anti-clockwise (the opposite direction)

46
Q

How can you improve the efficiency of a machine that uses gears?

A

Lubrication, reduce friction which will reduce energy loss through heat

Physics GCSE (7 decks)

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