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A-Level Physics > [AS] Forces and Energy > Flashcards

[AS] Forces and Energy Flashcards

1
Q

What is Newton’s First Law?

A

The velocity of an object will not change unless a resultant force acts on it

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2
Q

What is Newton’s Second Law?

A

Acceleration is proportional to resultant force

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3
Q

What is Newton’s Third Law?

A

Every force has an equal and opposite reaction force

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4
Q

What kind of friction acts between solid surfaces?

A

dry friction / contact friction

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5
Q

What kind of friction acts between fluid surfaces?

A

drag / fluid resistance / air resistance

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6
Q

What do you call a force that opposes motion?

A

Friction

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7
Q

What does friction convert kinetic energy into?

A

Heat and Sound

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8
Q

What is lift?

A

An upwards force on an object moving through a fluid.

It acts perpendicular to the direction of the fluid’s flow

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9
Q

What force acts perpendicular to the direction a fluid flows in?

A

Lift

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10
Q

What causes lift?

A

Fluid flowing changes direction as it moves over object’s shape

Difference in pressure on either side of the object

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11
Q

What two forces are equal at terminal velocity?

A

Friction and Driving Force

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12
Q

What are the two conditions for an object reach terminal velocity?

A
  1. a constant Driving Force

2. a Frictional Force that increases with speed

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13
Q

How can you increase a vehicle’s maximum speed?

A
  1. increase the Driving Force (increase engine size)

2. reduce the Frictional Force (more streamlined body)

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14
Q

Describe how a skydiver reaches terminal velocity

A
  1. Skydiver initially accelerates due to gravity
  2. Air resistance increases until it equals his weight (terminal velocity)
  3. The parachute opens, increasing air resistance
  4. He decelerates until he is slow enough for air resistance to equal weight
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15
Q

What does ‘resolving a force’ mean?

A

Splitting it into perpendicular components

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16
Q

What is always true for three coplanar forces acting on a point in equilibrium?

A

The three forces can be drawn as a closed triangle

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17
Q

For a force triangle, what is true about the direction of the forces?

A

You can trace their directions around the triangle in a loop

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18
Q

How do you find the resultant force of two component forces?

A

Add them together

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19
Q

What is density?

A

Mass per unit volume

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20
Q

What is an object’s density dependent on?

A

The material it is made of

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21
Q

Under what condition will a solid object float in a fluid?

A

If its density is lower than the fluid’s

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22
Q

What is pressure?

A

Force per unit area

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23
Q

What is pressure measured in?

A

pascals (Pa)

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24
Q

What is one pascal equivalent to?

A

Nm^-2

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25
What are the SI base units of the Newton?
kg⋅m⋅s^-2
26
What is the extra pressure on an object in a depth in a fluid equal to?
p = hρg
27
What is upthrust?
An upward force a fluid exerts on objects that are fully or partially submerged in the fluid
28
What is Archimedes' Principle?
Upthrust is equal to the weight of the displaced fluid
29
Does the mass of an object change when g changes?
No
30
Does the weight of an object change when g changes?
Yes
31
What is weight a measure of?
Force
32
What is weight equal to?
mg
33
Where should you assume all of the mass of an object acts?
Centre of mass
34
When will an object topple over?
If the centre of mass is outside its base
35
What is a moment?
The turning effect of a force
36
How do you calculate the moment?
Force × perpendicular distance from picot
37
What happens if the moments are imbalanced?
The object will turn
38
What is the principle of moments?
Sum of clockwise moments = sum of anticlockwise moments
39
What is a couple?
Two equal-size coplanar forces acting parallel to each-other in opposite directions
40
How do you calculate the moment of a couple?
Size of one of the forces × distance between them
41
How do you calculate momentum?
Mass × velocity
42
Is momentum conserved?
Yes
43
What is an elastic collision?
Momentum and kinetic energy are conserved
44
What is an inelastic collision?
Momentum is conserved Some kinetic energy is converted to other forms (e.g. sound)
45
What is impulse?
The change in momentum
46
How do you calculate impulse from a graph?
Area under a force-time graph
47
What is the area under a force-time graph?
Impulse
48
What is a Crumple zone?
An area at the front/rear of a car designed to crumple on impact
49
How does a Crumple zone reduce risk?
Absorb some of the car's kinetic energy | Increase time taken to slow down, reducing force
50
When is work done?
When energy is transferred?
51
What is done when energy is transferred?
Work
52
What happens to kinetic energy when an object stops moving?
It is transferred to another form of energy
53
Why do you need a force to move an object?
To overcome another force
54
Define work done
The amount of energy transferred from one form to another when a force causes movement
55
What is an equation for work done with force and distance?
Work done = Force × distance
56
How do you calculate work done from a graph?
Area under a force-displacement graph
57
What is the area under a force-displacement graph?
Work done
58
Define power
The rate that work is done | Energy transferred per second
59
What is the unit of Power?
Watt
60
What is kinetic energy?
Energy an object has due to movement
61
What is gravitational potential energy?
Energy an object has due to its position in a gravitational field
62
How is GPE related to Work?
GPE gained = | work done moving through a height
63
What is change in kinetic energy of an object equal to?
Work done on the object
64
What it the Principle of Conservation of Energy?
Energy can't be created or destroyed. It can only be transferred between forms
65
What is lost energy?
Energy transferred to a waste form
66
Is it possible for no energy to be lost?
No
67
What causes heat loss?
Friction
68
What is efficiency?
The ratio of useful energy output to total energy input

A-Level Physics (13 decks)

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