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GCSE AQA physics > Topic 5- Forces: > Flashcards

Topic 5- Forces: Flashcards

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1
Q

What is a vector?

A

Has both magnitude and direction

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2
Q

What is a scalar?

A

Only has magnitude.

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3
Q

What is a force?

A

A push or pull that acts on an object due to the interaction with another object.

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4
Q

What is an alternative name for the turning effect of a force?

A

A moment.

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5
Q

State the equation to calculate the moment of a force.

A

Moment of force (Nm) = force (N) x distance (m)

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6
Q

What distance measurment is used when calculating a moment?

A

The perpendicular diistance from the pivot to the line of action of the force.

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7
Q

If an object is in equilibrium, what can be said about the moments acting on the object?

A

The total clockwise moments= Total anticlockwise moments

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8
Q

What 3 parts make up a lever system?

A

1) Load
2) Effort
3) Pivot

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9
Q

How can a lever be used as a force multiplier?

A

If the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same.

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10
Q

Give an example of when a lever may be used to multiply a force?

A

A wrench, which has a long handle so that the force applied by the user is multiplied.

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11
Q

What determines the moment of a gear wheel?

A

The size of the wheel.

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12
Q

Describe the moment and speed of a larger gear being driven by a smaller gear.

A

The larger gear will rotate more slowly, but also produce a larger moment.

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13
Q

What does it mean if a force is said to ‘do work’?

A

The force causes an object to be displaced through a distance.

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14
Q

What is the equation for work done?

A

Work done (Joules) = Force (N) x distance (m)

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15
Q

What distance must be used when calculating work done?

A

The distance that is moved along the line of action of the force.

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16
Q

When is 1 joule of work done?

A

When a force of 1 Newton causes a displacement of 1 metre.

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17
Q

How many newton-metres are equal to 1 joule of energy?

A

1 Nm

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18
Q

What occurs when work is done against frictional forces?

A
  • The temperature of the object increases
  • Kinetic energy is converted to heat energy
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19
Q

Projectile- an object that is thrown/shot forward with force

Why does air resistance slow down a projectile ?

A
  • The object does work against air resistance.
  • Kinectic energy is converted into heat, slowing down the object.
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20
Q

How can a vector quantity be drawn and what does it show?

A
  • As an arrow
  • The length represents the magnitude (size)
  • The arrow points in the associated direction
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21
Q

What are the 2 categories that all forces can be split into?

A

1) Contact forces (objects touching)
2) Non-contact forces (objects that aren’t touching)

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22
Q

Give three examples of contact forces.

A

1) Friction
2) Air resistance
3) Tension

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23
Q

Give three examples of non-contact forces.

A

1) Gravitational forces
2) Electrostatic forces
3) Magnetic forces

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24
Q

Is force a vector or scalar quantity.

A
  • Vector
  • It has booth magnitude (size) and direction
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25
Q

Give three examples of vector quantities.

A

1) Velocity
2) Displacement
3) Force

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26
Q

Give some examples of scalar quantities.

A
  • Temperrature
  • Time
  • Mass
  • Speed
  • Distance
  • Energy
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27
Q

What is weight?

A

The force that acts on an object due to gravity and the object’s mass.

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28
Q

What quantities does weight depend on?

A
  • Weight = mass x gravitational field strength
  • The object’s mass
  • The gravitational field strength at the given position in the field
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29
Q

Whta is the unit used for weight.

A

The newton (N)

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30
Q

What is the unit for gravitational field strength.

A

N/kg

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31
Q

What does it mean by an object’s centre of mass?

A

The single point, where an object’s weight is considered to act through.

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32
Q

What peice of equipment can be used to measure an object’s weight?

A

A newton-metre.

33
Q

What is meant by the term ‘resultant force’?

A

The single force that is equivalent to all other forces acting on a given object.

34
Q

Explain the relationship between the force applied and the extension of an elastic object.

A

The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

35
Q

What is meant by inelastic (plastic) deformation?

A
  • A deformation which results in the object being permanently sretched
  • The object does not return to the original shape (when the force is removed)
36
Q

State the equation relating force, spring constant and extension.

A

Force (N) = Spring constant (N/m) x Extension (m)

37
Q

What type of energy is stored in an object when it is stretched?

A

Elastic potential energy.

38
Q

What can extension be replaced with in the equation for the force of a spring?

A

Compression

39
Q

What is meant by the term ‘fluid’?

A

A liquid or a gas

40
Q

In any fluid, what angles do the forces act due to pressure on a given surafce?

A

At right angles to the surface.

41
Q

State the equation for pressure.

A

Pressure (pascals) = Force (N) / Area (m^2)

42
Q

What happens to the density of the atmosphere with increasing altitude?

A

The atmosphere becomes less dense as altitude increases.

43
Q

Explain why atmospheric pressure decreases with increase height.

A
  • Pressure is created by a collision of air molecules
  • The quantity of molecules decreases as height increases
  • This means that atmospheric pressure decreases with an increase if height.
44
Q

What is the earth’s atmosphere?

A

A thin layer of gas surrounding the earth.

45
Q

How does pressure in fluids increase with depth?

A

As the depth increases, the mass of liquid above the depth also increases. This means that the force due to the mass also increases. Since the force has increased, whilst the area has remained constant, the pressure will increase.

46
Q

Why does pressure in fluids increase with density.

A

As the density of a fluid increases, the number of particles in a given volume also increases. Consequently, the weight of the fluid is greater. This means that the force from a fluid above a certain point is larger. Since the force increases, pressure also increases.

47
Q

Why are objects in a fluid subject to upthrust?

A

When an object is submerged in a fluid, it has a higher pressure below it than it does above, as there is more weight above it at the bottom than there is at the top. This leads to an upwards force called upthrust. You float or sink depending oon whether the upthrust is more or less than your weight.

48
Q

What is upthrust always equal to?

A

The weight of the fluid that the object displaces.

To displace- to forcefully remove.

49
Q

What factors will influence whether an object will sink or float?

A
  • Upthrust
  • Weight
  • Density of fluid
50
Q

Explain why an object with a density greater than that of water can never float.

A

Upthrust is equal to the weight of water that is displaced. If the density of the object is high, there would not be enough volume displaced to produce an upthrust larger than the object’s weight. This means that it will sink.

If density ⬆ mass ⬆ but volume ⬇

51
Q

If an object moves 3 metres to the left and then 3 metres back to it’s original position, what is the object’s total displacement?

A
  • The total displacement for the oject is 0
  • Displacement is a vector quantity, so it also involves direction
  • The object starts and ends at the same point, so it has not moved in a certain direction.
52
Q

What is the speed of sound?

A

330 m/s

53
Q

What is the human walking speed?

A

1.5 m/s

54
Q

What is the human running speed?

A

3 m/s

55
Q

What is the human cycling speed?

A

6 m/s

56
Q

Why can an object travelling at a constant speed in a circle not have constant velocity?

A
  • Speed is a scalar quanitity
  • Velocity is a vector quantity, so it can only be constant if the direction is constant
  • In a circuular motion, the object’s direction is constantly changing.
57
Q

How is speed calculated on a distance-time graph for an accelerating object?

A

The speed is the gradient.

58
Q

What must be done to calculate speed on a distance-time graph of an accelerating object?

A
  • Draw a tangent to the curve at the required time
  • Caluclate the gradient (speed)
59
Q

State the equation for accelearation.

A

Acceleration (m/s^2) = Velocity (m/s) / Time (s)

60
Q

How can the distance travelled by an object be calucated from a velocity-time graph?

A

The area under the graph represents the distance travelled.

61
Q

Give an approximate value for the acceleration of an object in free fall under gravity near the Earth’s surface.

A

9.8 m/s^2

62
Q

What can be said about the resultant force acting on an object when it is falling at terminal velocity?

A
  • The resultant force is 0
  • When at terminal velocity, the object is at a constant speed and so isn’t accelerating
63
Q

State Newton’s first law for a stationary object.

A

If the resultant force on a stationary objeect is 0, the object will remain at rest.

64
Q

State Newton’s first law for a stationary object.

A

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).

65
Q

What can be said about the braking forces and driving forces when a car is travelling at constant velocity?

A

The braking force are equal to the driving forces

66
Q

If an object changes direction, but remains at a constant speed, is there a resultant force?

A

Since there is a change in direction, there is a change in velocity, so there must be a resultant force.

67
Q

What is inertia?

A

The tendency of an object to continue at it’s statde of rest or uniform mtion.

68
Q

State the defining equation for Newton’s econd law.

A

Resultant force = Mass * Acceleration

69
Q

State Newton’s second law in words.

A

An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to it’s mass.

70
Q

What is inertial mass?

A
  • A measure of how difficult it is to change a givn object’s velocity.
  • The ratio of force over acceleration
71
Q

State Newton’s third law.

A

When two objects interact, they exert equal and opposite forces on eachother.

72
Q

What is the stopping distance of a vehicle equal to?

A

The sum of thinking distance and braking distance.

73
Q

For a given braaking distance, if the vehicle’s speed is increased, what can be said about it’s stopping distance?

A

The stopping distance is increased with an increase in speed.

74
Q

Give a typical range of values for human reaction time.

A

0.2 seconds- 0.9 seconds.

75
Q

Give three factors which can affect a driver’s reaction time.

A
  1. Drugs
  2. Alcohol
  3. Tiredness
76
Q

Give two factors which may affect braking distance.

A
  • Adverse (wet/icy) road conditions
  • Poor tyre/brake conditions
77
Q

Describe the energy transfers that take place when a car applies its brakes.

A
  • Work is done by the frictional force between the brakes and wheel
  • Kinetic eenergy of the wheel is converted to heat and is dissipated to thee surroundings through the brakes
78
Q

To stop a car in a given distance, if it’s velocity is increased, what must happen to the braking force applied?

A

The braking force may also be increased.

79
Q

State two consequences of a vehicle undergoing very large decelerations.

A

1) Kinetic energy is converted to heat is very high causing brakes to overheat
2) Loss of control over the vehicle

GCSE AQA physics (3 decks)

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