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IGCSE Physics > Forces And Their Effects > Flashcards

Forces And Their Effects Flashcards

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1
Q

What are scalar quantities?

A
  • They have magnitude only
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2
Q

What are vector quantities?

A
  • they have magnitude and an associated direction
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3
Q

List the scalar quantities:

A
  • speed
  • time
  • distance
  • temperature
  • mass
  • length
  • energy
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4
Q

List the vector quantities:

A
  • velocity
  • force
  • displacement
  • acceleration
  • momentum
  • weight
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5
Q

What is the formula for velocity?

A
  • velocity= displacement (distance in a given direction) / time taken
  • s = v x t
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6
Q

What does the gradient equal in a distance-time graph?

A
  • speed
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7
Q

What do the flat sections of a distance time graph represent?

A
  • stationary

- stopped

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8
Q

What do the curves represent in a distance time graph?

A
  • acceleration

- deceleration

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9
Q

What is acceleration?

A
  • how quickly the velocity is changing

- this change in velocity can be a change in speed or a change in direction (or both)

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10
Q

What is the formulae for acceleration?

A
  • acceleration = change in velocity / time taken

- a = (v - u) / t

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11
Q

What does the gradient represent in a velocity time graph?

A
  • acceleration
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12
Q

What do the flat section represent in a velocity time graph?

A
  • steady speed
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13
Q

What is a resultant force?

A
  • the overall force in a point or object

- whenever two objects interact, the forces they exert in each other are equal and opposite

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14
Q

What will happen to a stationary object if the resultant force was

1) zero
2) not zero

A

1) the object will remain stationary

2) the object will accelerate in the direction of the resultant force

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15
Q

What will happen to a moving object if the resultant force is

1) zero
2) not zero

A

1) the object will continue to move at the same speed and in the same direction
2) the object will accelerate in the direction of the resultant force

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16
Q

What is the equation to find the resultant force?

A
  • F = ma
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17
Q

What is momentum (p) ?

A

A property of moving objects

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18
Q

When is there more momentum?

A
  • the greater the mass of an object and the greater its velocity, the more momentum it has
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19
Q

Why is the equation for momentum?

A
  • p = m x v

- momentum (kg m/s) = mass (kg) x velocity (m/s)

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20
Q

What is the Conservation of Momentum?

A

In a closed system, the total momentum before an event is the same as after the event

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21
Q

What causes a change in momentum?

A
  • when a force acts on an object
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22
Q

What is the equation between force c change in momentum and time?

A
  • force acting (n) = change in momentum (kg m/s) / time take for change to happen (S)
  • 🔼p = F x t
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23
Q

Why do safety features in a car increase the collision time?

A
  • this decreases the rate of change of momentum and so reduces the forces on the passengers
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24
Q

What do seat belts do?

A
  • seat belts stretch slightly, increasing the time taken for the wearer to stop
  • this decreases the rate of change of momentum and so reduces the forces acting in the chest
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25
Q

What to air bags do?

A
  • slow us down more gradually
  • decreases the rate of change of momentum
  • reduces the forces acting on the chest
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26
Q

Why would an object with no force propelling it along always slow down and stop?

A
  • because of friction
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27
Q

What direction does friction act?

A
  • the opposite direction of movement
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28
Q

How can you travel at a steady speed?

A
  • the driving force needs to balance the frictional forces
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29
Q

What happens to frictional forces/drag with speed increases?

A
  • they also increase
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30
Q

Why do objects falling through fluids reach a terminal velocity?

A
  • when falling objects first set off, the force of gravity is much more than the frictional force slowing them down
  • so they accelerate.
  • as the speed increases the friction builds up
  • this gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force
  • then it will have reached terminal velocity and fall at a steady speed
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31
Q

What is a total stopping distance?

A
  • the distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop
  • the sum of the thinking distance and the braking distance
32
Q

What is thinking distance?

A
  • the distance the vehicle travels during the driver’s reaction time
33
Q

What factors affect thinking distance?

A
  • how fast you’re going: faster you go, further you’ll go
  • tiredness, drugs, alcohol, carelessness.
  • bad visibility and distractions.
34
Q

What is braking distance?

A
  • the distance the car tracked under the braking force
35
Q

What factors affect braking distance?

A
  • how fast you’re going: faster you’re going, further it takes to stop
  • how good brakes are
  • how good tyres are: need a minimum tread depth of 1.6mm
  • how good grip is: depending on road surface, weather conditions and tyres
36
Q

What is weight?

A
  • weight is caused by the pull of the gravitational force
37
Q

What is the Formula for weight?

A
  • W = m x g

- weight = mass x gravitational field strength

38
Q

What happens when a force moved an object through a distance?

A
  • energy is transferred

- work is done

39
Q

What is the formula for work done?

A
  • work done = force x distance

- W = F x d

40
Q

What is gravitational potential energy (measured in joules)?

A
  • it is the energy that an object has by virtue of its vertical position in a gravitational field
  • when an object is raised vertically, work is done against the force of gravity and the object gains GPE
  • gravitational field strength is approx 10N/kg on earth
41
Q

What the formula for gravitational potential energy?

A
  • GPE = mass x g x h

- Ep = m x g x h

42
Q

What is kinetic energy?

A
  • the energy of movement
43
Q

What is the formula for kinetic energy?

A
  • kinetic energy = 1/2 x mass x speed^2

- Ek = 1/2 x m x v^2

44
Q

What is work done?

A
  • The transfer of kinetic energy
45
Q

What is the equation for kinetic energy transferred?

A
  • kinetic energy transferred = work done by brakes

- 1/2mv^2 = F x d

46
Q

What is work done to an elastic object stored as?

A
  • elastic potential energy
  • when a force is applied to an object you may stretch it and it may change in shape.
  • it is stored as EPE
47
Q

What happens when an elastic object is extended?

A
  • the extension, e, of a stretched spring is directly proportional to the lord or force applied , F.
  • F = k x e
  • k is the spring constant. Measured in N/m
48
Q

What is the limit of proportionality ?

A
  • there is a maximum force that the elastic object can take and still experience proportionally.
  • this is known as the limit of proportionality.
49
Q

What is power?

A
  • power is the rate of doing work
  • measured in watts
  • one watt = 1 joule of energy transferred lee second
50
Q

What is the formula for power?

A
  • Power = work done (or energy transferred) / time taken

- P = W / t

51
Q

What is the time period of a pendulum?

A
  • the time taken for the pendulum to swing from one side to the other and back again
52
Q

Why are pendulums perfect for keeping time in clocks?

A
  • the time period for each swing of a pendulum is always the same
53
Q

What formula can calculate time worked?

A
  • Time period = 1 / frequency

- T = 1 / f

54
Q

What does the time period depend on?

A
  • the length

- the longer the pendulum, the greater the time period

55
Q

What is circular motion?

A
  • if an object is travelling in a circle it is constantly changing direction
  • this means velocity is constantly changing (but not speed)
  • so object is accelerating, towards the centre of the circle.
56
Q

What is centripetal force?

A
  • the force that keeps something moving in a circle

- the resultant force acting on the object causing acceleration

57
Q

When does the centripetal force needed to make an object perform circular motion increase?

A
  • as the mass of the object increases
  • as the speed of the object increases
  • as the radius of the circle decreases
58
Q

What is the centre of mass?

A
  • the centre of mass of an object is the point at which the mass of the object seems to be concentrated
59
Q

Where will an object come to rest if free suspended?

A
  • at its centre of mass directly below the point of suspension
60
Q

Where is the centre of mass of a symmetrical object?

A
  • along the axis of symmetry
61
Q

What is the equation for the size of a moment?

A
  • moment = force x perpendicular distance from the line of action of the force to the pivot
  • M(Nm) = F(N) x d(m)
62
Q

What is the moment?

A
  • the turning effect of a force
63
Q

Why would using a longer spanner exert a larger moment?

A
  • the distance from the pivot is greater

- less force is needed to get the same moment

64
Q

How do you get the maximum moment?

A
  • push at right angles (perpendicular) to the spanner
65
Q

What happens when an object is not turning?

A
  • the total clockwise moment must be at equilibrium with the total anticlockwise moment at any pivot
66
Q

What are simple levers known as?

A
  • force multipliers

- they reduce the amount of force that’s needed to get the same moment by increasing the distance

67
Q

Give three examples of simple levers

A
  • long sticks or bars
  • wheelbarrows
  • scissors
68
Q

What makes an object stable?

A
  • a wide base

- a low centre of mass

69
Q

What makes an object tip over?

A
  • if the line of action of the weight of the object lies outside the base of the object, it will cause a resultant movement
  • therefore it tips over
70
Q

Can liquids be compressed?

A
  • no, they are virtually incompressible
71
Q

What happens when a force is applied to one point in the liquid?

A
  • it will be transmitted to the other point in the liquid

- pressure in a liquid is transmitted equally in all directions

72
Q

Give the equation for pressure

A
  • Pressure = Force x cross-sectional area

- F(N) = P(Pa) x A (m^2)

73
Q

What are hydraulic systems used as?

A
  • force multipliers
74
Q

What are the two pistons in a hydraulic system?

A
  • master piston: smaller cross-sectional area

- slave piston: larger cross sectional area

75
Q

Describe how a simple hydraulic system works

A
  • at the master piston, the pressure is exerted on the liquid using a small force over a small area
  • this pressure is transmitted to the slave piston
  • the slave piston has a larger area, so due to F = P x a, there will be a larger force
76
Q

What are hydraulic systems used for?

A
  • car braking systems
  • hydraulic car jacks
  • manufacturing and deployment of landing gear on some aircraft

IGCSE Physics (8 decks)

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