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A Level Physics Year 1 > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

What is a scalar quantity?

A

A quantity that has no direction (just an amount)

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2
Q

What is a vector quantity?

A

A quantity that has magnitude and direction

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3
Q

Give 4 examples of scalar quantities

A

Mass
Temperature
Energy
Distance

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4
Q

Give 4 examples of vector quantities

A

Acceleration
Velocity
Momentum
Displacement

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5
Q

What is a bearing?

A

A 3-digit angle that is measured clockwise from north in degrees

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6
Q

How do you find the resultant vector?

A

By adding 2 or more vectors together

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7
Q

How do you find the resultant vector from a scale diagram?

A

Drawing a scale diagram with all the vectors joining in one line (tip-to-tail), then measuring the length and angle of the resultant vector from the diagram

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8
Q

What is displacement?

A

The position relative to the start position

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9
Q

What does cos60 and sin30 equal?

A

0.5

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10
Q

What is an inclined plane?

A

A slope

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11
Q

Which direction does weight always act?

A

Downwards

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12
Q

What is happening when is a body is in equilibrium?

A

All the forces are balanced (no resultant force)

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13
Q

What 2 states can an object in equilibrium be at?

A

Rest or moving with constant velocity

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14
Q

When only 2 forces act on an object, what do they have to be for the object to be in equilibrium?

A

Equal and opposite (opposite direction)

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15
Q

When forces act on an object in equilibrium, what do they form if you draw them tip-to-tail in a scale diagram?

A

Form a closed loop (a vector triangle)

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16
Q

What is the magnitude of a vector?

A

The size of it (without direction)

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17
Q

What is a moment of a force?

A

The turning point of a force around a point

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18
Q

What are 2 moments of equal size acting parallel to each other called?

A

A couple

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19
Q

What is the mass of an object defined as?

A

The amount of matter in it

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20
Q

What is inertia?

A

A resistance to a change in motion

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21
Q

What happens to the inertia if an objects mass is increased?

A

The greater the resistance to a change in motion will be (larger inertia)

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22
Q

What is weight and what is it measured in?

A

A force measured in newtons

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23
Q

Define weight

A

The force experienced by a mass due to gravity

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24
Q

What equation links weight, gravity field strength and mass

A

W=mg

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25
Q

Is weight a scalar or vector quantity?

A

Vector as it has size and direction

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26
Q

What 2 things does the moment of a force depend on?

A

Size of the force and how far the force is applied from the turning point

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27
Q

What equation links moment, force and perpendicular distance from the turning point?

A

M = fd

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28
Q

What does the principle of moment state for a body to be at equilibrium?

A

The sum of the clockwise moments about any point equals the sum of the anti-clockwise moments at the same point

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29
Q

What will happen to an object if the moments aren’t balanced?

A

The object will turn

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30
Q

How do levers work?

A

An effort force acts against a load force by means of a rigid object rotating around a pivot

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31
Q

What situations are levers useful in?

A

If you need a larger turning effect

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32
Q

Give 3 examples of levers

A

Spanners
Wheelbarrows
Scissors

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33
Q

How does a spanner (or any other lever) work?

A

They increase the distance from the pivot a force is applied, so you need less force to get the same moment

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34
Q

What does ‘Σ’ mean?

A

The sum of

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35
Q

What is a couple?

A

A pair of forces of equal size which act parallel to each other, but in opposite directions

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36
Q

What does a couple cause?

A

A turning effect (moment), doesn’t cause any resultant linear force

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37
Q

What is an object’s centre of mass?

A

The single point that it’s whole weight acts through (whatever the orientation)

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38
Q

What will an object at centre of mass do?

A

Balance

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39
Q

For a uniform regular solid, where is the centre of mass?

A

In the centre

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40
Q

What are the 4 steps to find an objects centre of mass?

A
  • Hang the object freely from a point
  • Draw a vertical line downwards from the point of suspension
  • Hang the object from a different point and draw a line downwards
  • Centre of mass is where the 2 lines cross
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41
Q

Why will an object topple over?

A

If the line of action of its weight falls outside it’s base area

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42
Q

Why does it cause an object to topple over if the line of action of its weight falls outside it’s base area?

A

A resultant moment occurs, which provides a turning force

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43
Q

What cause an object to be less stable?

A

If the centre of mass is higher, and there is a small base area

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44
Q

What makes an object very stable?

A

If it has a low centre of mass and a wide base area

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45
Q

If an object is being held up on supports (e.g. a chair), why is the force acting on each support not the same?

A

the closer the centre of mass is to a support, the stronger the force on that support

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46
Q

What is speed?

A

How fast something is moving, regardless of direction

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47
Q

What is displacement?

A

How far an object has travelled from its starting point in a given direction

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48
Q

What is velocity?

A

The rate of change of an object’s displacement (it’s speed in a given direction)

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49
Q

What is acceleration?

A

The rate of change of an object’s velocity

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50
Q

What does the U mean in the SUVAT equations?

A

Initial velocity (ms^-1)

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51
Q

In displacement-time graphs, what is plotted on the Y-axis?

A

Displacement

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52
Q

What does the gradient of a displacement-time graph show?

A

Velocity

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53
Q

What does a steeper gradient in a displacement-time graph mean?

A

A bigger acceleration

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54
Q

What is the equation linking velocity, change in displacement and time taken?

A

Velocity = Change in displacement / Time taken

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55
Q

What is an object’s instantaneous velocity?

A

It’s velocity at a particular moment in time

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56
Q

How did you find the instantaneous velocity of an object from a displacement-time graph?

A

At a given point, draw a tangent to the graph and find the gradient of it

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57
Q

What is the average velocity?

A

The total change in displacement of the object divided by the total time taken

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58
Q

What does the gradient of a velocity-time graph?

A

Acceleration

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59
Q

What does a steeper gradient on a velocity-time graph mean?

A

A greater acceleration

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60
Q

What is the difference between velocity-time graphs and speed-time graphs?

A

Velocity-time graphs can have negative regions to show something travelling in the opposite direction

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61
Q

What is the area under a speed-time graph equal to?

A

Distance travelled

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62
Q

What does a straight line on a velocity-time/speed-time graph represent?

A

A uniform acceleration or deceleration

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63
Q

When is a situation where you can’t use the SUVAT equations?

A

If the acceleration isn’t constant

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64
Q

How do you find the acceleration at a point on a velocity-time graph with changing acceleration?

A

Draw a tangent at that point and find the gradient of the tangent

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65
Q

What are 3 main advantages of using dataloggers over traditional methods?

A

The data is more accurate as you don’t have to allow for human reaction times
Automatic systems have a much higher sampling rate than humans
You can see the data displayed in real time

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66
Q

What does the height at any point on an acceleration-time graph show?

A

The acceleration at that time

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67
Q

What does it mean if a=0?

A

Constant velocity

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68
Q

What does a negative gradient (above the x-axis) mean on an acceleration-time graph?

A

It means the object is still accelerating, but the rate of acceleration is decreasing

69
Q

What is the area under an acceleration-time graph equal to?

A

The total change in velocity

70
Q

What does Newton’s 1st law of motion state?

A

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

71
Q

What does Newton’s 1st law of motion mean?

A

A body will stay still or move in a straight line at a constant speed, unless there’s a resultant forces acting on it

72
Q

Why won’t an apple sitting on a table move?

A

Because the forces are balanced. Reaction (force of table pushing up on apple) = Weight (force of gravity pulling apple down)

73
Q

What is Newton’s 2nd law of motion?

A

The acceleration of an object is proportional to the resultant force acting on it

74
Q

What equation defines Newton’s 2nd law?

A

F = ma

75
Q

What 2 things can we see from the equation F = ma?

A

The more force you have acting on a certain mass, the more acceleration you get
For a given force, the more mass you have, the less acceleration

76
Q

What is the resultant force?

A

The vector sum of all the forces

77
Q

What is the resultant force always measured in?

A

Newtons

78
Q

What is Newton’s 3rd law of motion?

A

If an object A exerts a force on object B, then object B exerts an equal but opposite force on object A

79
Q

What situations can Newton’s 3rd law be used?

A

All situations, but both forces have to be the same (e.g. both gravitational)

80
Q

What is freefall?

A

When there’s gravity acting on an object and nothing else

81
Q

Freefall is defined as…?

A

The motion of an object undergoing an acceleration, g

82
Q

What type of quantity is acceleration?

A

Vector

83
Q

What is the only force acting on an object in freefall?

A

It’s weight

84
Q

What did Galileo prove in his experiments?

A

That all objects fall at the same rate, and he showed mathematically that all objects are attracted towards the Earth due to a force called gravity

85
Q

Why do all objects fall at the same rate (not accounting for air resistance)?

A

The acceleration is independent of the mass (mass makes no difference)

86
Q

What is the sign convention for upwards and downwards when calculating motion?

A

Upwards is +ve and downwards is -ve

87
Q

What direction does g act?

A

Downwards so it’s normally a negative number in calculations

88
Q

How do you set up the experiment for determining g using freefall method?

A

Put a trapdoor on the floor and measure a set distance up. At this distance, position an electromagnet with a ball bearing. Attach a timer and a switch in series with the electromagnet, and connect the trapdoor to the circuit

89
Q

What are the 5 steps for the experiment to determine the value of g by freefall method?

A
  • Measure the height, h, from the bottom of the ball bearing to the trapdoor
  • Flick the switch to simultaneously start the timer and release the ball bearing
  • When the ball bearing falls, it hits the trapdoor, thus breaking the circuit, so the timer will stop. Record the time, t, shown on the timer
  • Repeat experiment 3 times and then average the time taken for the ball bearing to drop
  • Use these results to find the value of g from a graph
90
Q

What is the most significant source of random error for the experiment to determine g from freefall method?

A

Measurement of h, as the ruler will have an uncertainty of +- 1mm

91
Q

In the experiment to determine g from freefall method, why would you use a small, heavy ball bearing?

A

Because we can then assume that air resistance is negligible

92
Q

What is projectile motion?

A

Motion with a constant horizontal velocity and a vertical velocity affected by acceleration due to gravity

93
Q

In projectile motion, the horizontal and the vertical velocity are…?

A

Independent of each other

94
Q

Why do projectiles follow a curved path?

A

Because their horizontal velocity is constant, but their vertical velocity increases due to gravity

95
Q

For projectiles, describe the horizontal acceleration and velocity

A 
Acceleration = 0
Velocity = Constant
96
Q

For projectiles, describe the vertical acceleration and velocity

A 
Acceleration = -9.81ms^-1
Velocity = Changes with time according to equation V=U+AT
97
Q

What are the 3 steps for solving projectile motion problems with an angle?

A
  • Resolve the initial velocity into horizontal and vertical components
  • Use the vertical component to work out how long it’s in the air/how high it goes
  • Use the horizontal component to work out how far it goes in the horizontal direction
98
Q

When resolving vectors, how do you calculate the vertical component?

A

Vy = Vsinθ

99
Q

When resolving vectors, how do you calculate the horizontal component?

A

Vx = Vcosθ

100
Q

Air resistance causes a….that acts in the…..direction to motion and affects the trajectory of a projectile

A

Air resistance causes a drag force that acts in the opposite direction to motion and affects the trajectory of a projectile

101
Q

What is the effect of the horizontal component of drag?

A

Reduces the horizontal speed of the projectile and reduces the horizontal distance it travels

102
Q

What is the effect of the vertical component of drag?

A

Reduces the maximum height the projectile will reach and steepens the angle of descent

103
Q

What is friction?

A

A force that opposes motion

104
Q

What are the 2 main types of friction?

A

Contact friction

Fluid friction

105
Q

What is contact friction?

A

Friction that occurs between solid surfaces

106
Q

What is fluid friction?

A

Friction when it’s in gas or liquid, such as air resistance. Also known as drag

107
Q

What 3 things affect fluid friction?

A
  • The force depends on the viscosity of the fluid
  • The force increases as speed increases
  • The forces depends on the shape of the object moving through it
108
Q

What are the 3 main things about frictional forces?

A
  • They act in the opposite direction to the motion of the object
  • They can never speed up or start something moving
  • They convert kinetic energy into heat
109
Q

What is lift?

A

An upwards force on an object moving through a fluid

110
Q

What causes lift?

A

When the shape of an object causes the fluid flowing over it to change direction (such as an aircraft wing)

111
Q

What direction does lift force work at?

A

Perpendicular to the direction in which the fluid is flowing

112
Q

How does a plane wing cause lift?

A

As the wing moves through the air, it pushes down on the air (and changes it’s direction). This causes an equal and opposite reaction force on the wing

113
Q

What is terminal velocity?

A

The speed at which the driving force(s) match the frictional force(s) (and so the resultant force becomes 0)

114
Q

When will an object reach terminal velocity?

A

When the driving forces stays constant, but the frictional force increases with speed

115
Q

What happens to the air resistance on an object when speed increases?

A

Air resistance on an object increases with speed

116
Q

What are 2 ways of increasing a vehicle’s maximum speed?

A

Increasing the driving force (e.g. larger engine)

Reducing the frictional forces (e.g. more aerodynamic)

117
Q

On a velocity-time graph, what feature of the graph shows that the object has reached terminal velocity?

A

A gradient that equals 0 from a steady increasing gradient

118
Q

Describe what happens when an object falling through the air reaching terminal velocity

A

The weight of the object is a constant force of acceleration downwards. Air resistance is a frictional force opposing this motion, which increases with speed. The object reaches a point where the resistance forces are equal to the driving force, so it reaches terminal velocity

119
Q

What is the equation for momentum?

A

Momentum = Mass x Velocity

120
Q

What type of quantity is momentum, scalar or vector?

A

Vector

121
Q

What is momentum?

A

It’s the product of an object’s mass and velocity

122
Q

What is the SI unit of momentum?

A

kg ms^-1

123
Q

What is the equation for density?

A

Density = Mass/Volume

124
Q

Assuming no external forces act, linear momentum is always…?

A

Conserved

125
Q

What is the total linear momentum of 2 objects before they collide equal to?

A

The total linear momentum after the collision

126
Q

Explain what happens when you fire a rifle in terms of the principle of linear momentum

A

The forward momentum gained by the bullet is equal in magnitude to the backward momentum of the rifle (the recoil)

127
Q

What is an elastic collision?

A

A collision where momentum is conserved and kinetic energy is conserved

128
Q

What is kinetic energy?

A

The energy an object has due to its motion

129
Q

What is the equation for kinetic energy?

A

Ek = 0.5 mv^2

130
Q

What does it mean if a collision is inelastic?

A

Some of the kinetic energy is converted into other forms during the collision

131
Q

What is the SI units for rate of change of momentum?

A

kg ms^-2

132
Q

What is force equal to in terms of momentum?

A

Force = Change in momentum = Δ(mv)/ Δt

133
Q

What equation links change in momentum, mass, initial velocity and final velocity?

A

Δ(mv) = mv - mu

134
Q

What is impulse?

A

The impulse acting on an object is equal to the change in momentum of the object

135
Q

What is the SI unit of impulse?

A

Ns

136
Q

What is impulse defined as?

A

The product of force and time

137
Q

What represents impulse on a force-time graph?

A

The area under the graph

138
Q

How can you reduce the force of an impact?

A

By increasing the time of the impact, as force = change in momentum

139
Q

How can the force of an impact be increased?

A

By reducing the time of the impact

140
Q

What are 3 safety features that cars have to decrease the force of a crash?

A

Crumple zones
Seat belts
Airbags

141
Q

How do crumple zones on a car work?

A

The parts of the car at the front and back crumple up and deform plastically on impact. This causes the car to take longer to stop, increasing the impact time and decreasing the force on the passengers

142
Q

How do seat belts work?

A

They stretch slightly, increasing the time taken for the wearer to stop, thus decreasing the force

143
Q

How do airbags work?

A

They slow down the passengers more gradually, and prevent them from hitting any hard objects

144
Q

Work is done whenever…?

A

… energy is transferred

145
Q

What does work mean in physics terms?

A

The amount of energy transferred from one form to another when a force causes a movement of some sort

146
Q

What is the equation for work done?

A

Work done = force x distance

W=Fs

147
Q

What does 1 joule mean?

A

The work done when a force of 1 newton moves an object through a distance of 1 metre

148
Q

What is the equation for work done when the force is at an angle?

A

W = Fs cosθ

θ = angle the line of action of the force makes with direction of motion

149
Q

What is power?

A

The amount of energy transferred from one form to another per second

150
Q

What is the equation linking power, work done and time?

A

P = (ΔW)/(Δt)

151
Q

What is a watt defined as?

A

Rate of energy transfer, equal to 1 joule per second

152
Q

What is the area under a force-displacement graph equal to?

A

Work done

153
Q

Why can’t you use the equation W=Fs for a variable force?

A

Because the force isn’t constant

154
Q

What is the equation linking power, force, speed and angle at which the force acts to the direction of motion?

A

P = Fv cosθ

155
Q

What does the principle of the conservation of energy state?

A

Energy cannot be created or destroyed, only transferred from one form to another (total amount of energy stays the same in a closed system)

156
Q

What is efficiency?

A

The ratio of useful energy given out by a machine to the amount of energy put into a machine

157
Q

What is the equation for efficiency of energy?

A

Efficiency = Useful energy output / Energy input

158
Q

What is the equation for efficiency of power?

A

Efficiency = Useful power output / Power input

159
Q

What is kinetic energy?

A

The energy of anything moving

160
Q

What is the equation for kinetic energy?

A

Ek = 0.5mv^2

161
Q

What is a kJ equal to?

A

1000J

162
Q

When an object is falling, what type of energy does it lose?

A

Gravitational potential

163
Q

What is gravitational potential energy?

A

The energy something gains when you lift it up in a gravitational field

164
Q

What is the equation for gravitational potential energy?

A

Ep = mass x gravity field strength x height

165
Q

What is elastic potential energy?

A

The energy stored in a stretched material

166
Q

What is the equation for elastic potential energy?

A

E = 0.5 x spring constant x extension^2

167
Q

Describe the energy transfers that occur when you throw a ball up

A

Kinetic energy is transferred to gravitational potential energy

168
Q

Describe the energy transfers that occur when a ball is falling towards the ground

A

Gravitational potential energy is transferred to kinetic energy

169
Q

If you’re ignoring frictional forces, what is the equation to use for solving problems with energy conservation?

A

Change in potential energy = Change in kinetic energy

mgh = 0.5mv^2

A Level Physics Year 1 (7 decks)

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