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Physics paper 2 > Forces > Flashcards

Forces Flashcards

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1
Q

Difference between scalar and vector quantities

A

Vectors quantities have an associated direction and magnitude
Scalar quantities have magnitude only

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2
Q

How may a vector quantity be presented

A
  • Presented as an arrow
  • Direction of the arrow shows the direction
  • Size of the arrow shows the magnitude
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3
Q

Give three examples of vector quantities

A
  • Velocity
  • Displacement
  • Force
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4
Q

Give five examples of scalar quantities

A
  • Temperature
  • Time
  • Mass
  • Distance
  • Speed
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5
Q

What is a force

A

A push or pull that acts on an object due to the interaction with another object.
Can be either non contact or contact
Force is a vector quantity

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6
Q

Give three examples of non contact and contact forces

A

Non contact :
- Gravitational forces
- Electrostatic forces
- Magnetic forces

Contact:
- Friction
- Tension
- Air resistance

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7
Q

What is weight

A

Weight is the force on an object due to gravity
The weight of an object depends on the gravitational field strength at the point where the object is

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8
Q

What is an objects centre of mass

A

The single point where the weight of an object acts upon

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9
Q

What is the relationship between the weight and mass of an object

A

Directly proportional

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10
Q

What measures weight

A

Calibrated spring balance (a newton-meter)

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11
Q

What is the resultant force of an object

A

A single force that has the same effect as all the original forces acting together.

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12
Q

What is meant when a force is said to do ‘work’

A

The force causes an object to be displaced through a distance

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13
Q

What is meant by an isolated system

A

Don’t need to worry about external forces associated with the surroundings

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14
Q

What is one joule equal to, and why?

A

One newton-meter
Because one joule of work is done when a force of one newton causes a displacement of one meter

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15
Q

What causes a rise in the temperature of the object.

A

When work is done against the frictional forces acting on an object

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16
Q

Why does air resistance slow down a projectile?

A
  • the object does work against the air resistance
  • Kinetic energy is converted into heat, slowing down the object
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17
Q

Explain why, to change the shape of an object (by stretching,
bending or compressing), more than one force has to be
applied

A

Because a single force would simply cause the object to move in the direction in which the force were to be applied

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18
Q

Describe the difference between elastic deformation and
inelastic deformation caused by stretching forces

A

Elastic deformation is reversed when the force is removed
Inelastic deformation is not fully reversed when the force is removed - there is a permanent change in shape

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19
Q

What is the relationship between extension and force applied
(Hooke’s Law)

A

Directly proportional, provided that the limit of proportionality is not exceeded

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20
Q

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

A

Compression

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21
Q

Describe the difference between a linear and non-linear
relationship between force and extension

A

If an object doesn’t obey Hooke’s law, there is a non-linear relationship between force and extension

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22
Q

investigate the relationship between force and extension for a
spring
Set up method (6 marks)

A
  • Set up equipment, ensure spring can return to its original dimensions. 2 clamp stands, one with spring and one with a ruler
  • Measure initial length of spring without any weights
  • Add a 10g mass to the base of the spring and record length of spring
  • Repeat and keep adding masses, ensuring spring doesnt oscillate
  • Convert all masses to weights (using Weight(N) = Mass(kg) x 9.81)
  • Plot the graph of force (y-axis) against extension (x axis) and calculate gradient
  • If the spring obeys Hooke’s law it will be a linear graph going through origin
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23
Q

What is a moment

A

Turning effect of a force

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24
Q

What distance measurement is used when calculating a moment

A

The perpendicular distance from the pivot line to the line of action of the force

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25
Q

What three parts make up a lever system?

A

1- Load
2- Effort
3- Pivot

26
Q

How can a lever be used as a force multiplier?

A

A moment is the turning effect of a force and is calculated by force*distance
Force stays constant and the distance increases therefore the turning effect increases proportionally to the increase of distance

27
Q

When should the total clockwise moment about a pivot
equals the total anticlockwise moment about that pivot

A

When the object is balanced

28
Q

What determines the moment of a gear wheel

A

The size of the wheel

29
Q

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

A

The larger wheel will rotate more slowly but also produce a larger moment

30
Q

What is a fluid

A

Gas or liquid

31
Q

What does the pressure in fluids cause

A

A force normal (at right angles) to any surface

32
Q

What happens to the density of the atmosphere with increasing atmosphere

A

Atmosphere becomes less dense as altitude increases

33
Q

Explain why atmospheric pressure decreases with an increase in height

A
  • Pressure is created by collisions of air particles
  • Quantity of air molecules decreases as the height increases
  • This means atmospheric pressure decreases with an increase in height
34
Q

What is the Earth’s atmosphere

A

A relatively thin layer of gas surrounding the earth

35
Q

How does pressure in fluids increase with depth?

A
  • As the depth increases, the mass of liquid above that depth also increases.
  • The force due to mass increases
  • Since the force has increased whilst the area has remained constant, the pressure will increase
36
Q

Why does pressure in fluids increase with density?

A

Because as there are more particles in a given space and since mass=density*volume a greater density means a higher mass, a higher mass results in a greater force of weight and since pressure = force/area if force is increased and area is constant the pressure must also increase

37
Q

What is upthrust always equal to

A

The weight of the fluid that the object displaces

38
Q

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

A

Upthrust is equal to the weight of the fluid that the object displaces.
If the density of the object is high, there will not be enough volume displaced to produce an upthrust larger than the objects weight
So it will sink

39
Q

State a typical value for the speed of sound

A

330 m/s

40
Q

State a typical value for human walking speed

A

1.5m/s

41
Q

State a typical value for human running speed

A

3m/s

42
Q

State a typical value for human cycling speed

A

6m/s

43
Q

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

A
  • Velocity is a vector quantity which means it can only be constant if the direction is constant
  • In circular motion, the direction is continually changing
44
Q

Give a value for the acceleration of an object in free fall under gravity near the earths surface

A

9.8m/s^2

45
Q

State newtons first law

A

An object remains in the same state of motion unless a resultant force acts on it

46
Q

State newtons second law

A

Resultant force = mass × acceleration

47
Q

State newtons third law

A

Whenever two objects interact, the forces that they exert on each other are always equal and opposite

48
Q

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

A

The braking forces are equal to the driving forces

49
Q

What is inertia

A

The tendency of an object to continue in its state of rest or uniform motion

50
Q

What is inertial mass

A
  • A measure of how difficult it is to change a given object’s velocity
  • The ratio of force over acceleration
51
Q

What is the stopping distance of a vehicle equal to

A

The sum of thinking distance and braking distance

52
Q

Give a typical range of values for human reaction time

A

0.2 secs - 0.9 secs

53
Q

Three factors that can affect a driver’s reaction time

A
  • Tiredness
  • Drugs
  • Alcohol
54
Q

Give two factors which may affect braking distance

A
  • Adverse road conditions
  • Poor tyre/brake conditions
55
Q

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

A
  • Work is done by the friction force between the brakes and wheel
  • Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs
56
Q

State two consequences of a vehicle undergoing very large decelerations

A

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

57
Q

What is the unit of momentum

A

kg m/s

58
Q

In a closed system, what can be said about the momentum before and after a collision

A

Total momentum before is equal to the total momentum afterwards

59
Q

What quantity is equal to the force experienced in a collision?

A

The rate of change of momentum

60
Q

Explain how a seatbelt improves a passenger’s safety during a collision

A
  • Both car and the passenger are moving at the same speed
  • The brakes stop the car moving
  • Brakes only work on the car, so will not stop the passenger moving
  • Objects remain in motion unless acted upon by an external force
  • Seat belt is needed to stop continuous movement of passenger forwards

Physics paper 2 (4 decks)

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