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[GCSE] physics > P5: FORCES > Flashcards

P5: FORCES Flashcards

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1
Q

What is a scalar quantity and give three examples

A

It is a physical quantity which has magnitude (size) only. For example: time, voltage , energy

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2
Q

What is a vector quantity? Give three examples

A

It has a magnitude and a direction. For example:
velocity, force, displacement

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3
Q

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

A
  • as an arrow
  • length of arrow = the magnitude
  • the arrow points in the associated direction
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4
Q

what is a force? Give the two types

A
  • a push or pull acting on an object due to an interaction with another object
  • contact forces
  • non-contact forces
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5
Q

give three examples of contact forces

A
  1. friction
  2. Air resistance
  3. Tension
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6
Q

give three examples of non-contact forces

A
  1. gravitational forces
  2. electrostatic forces
  3. magnetic forces
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7
Q

Give three examples of vector quantities

A
  1. velocity
  2. Displacement
  3. Force
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8
Q

Give 5 examples of scalar quantities

A
  • temperature
  • time
  • mass
  • speed
  • distance,
  • energy
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9
Q

what is weight?

A

Weight is the force acting on an object due to
gravity.

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10
Q

what quantities does weight depend on? Include equation and units

A

Weight = mass x gravitational field strength
- The object’s mass
- the gravitational field strength at the given position in the field
weight: Newtons , N
g = Newtons per kilogram , N/kg

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11
Q

What is the meant by an object’s centre of mass?

A
  • the single point where an object’s weight can be considered to act through
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12
Q

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

A
  • a calibrated spring-balance or newton-metre
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13
Q

define ‘ the resultant force’

A
  • the name given to the single force that is equivalent to all the other forces acting on a given object
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14
Q

State the effect of balanced forces on
an object’s motion.

A
  • a stationary object stays still
  • a moving object continues to move at
    the same speed and in the same
    direction
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15
Q

Describe how stationary and moving objects move when a resultant force acts.

A
  • a stationary object starts to move in the
    direction of the resultant force
  • a moving object changes speed and/or
    direction in the direction of the
    resultant force
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16
Q

What does it mean to “resolve a
force”?

A

A single force can be resolved into two
components acting at right angles to each
other. The two component forces together have the same effect as the single force.

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17
Q

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

A

A force does work on an object when the force causes a displacement of the object.

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18
Q

What is the equation used to calculate work done? Give appropriate units.

A

Work done = Force x distance
work done = joules
force = newtons
distance= metres

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19
Q

Wat distance must be used when calculating work done?

A
  • it must be the distance that is moved along the line of action of the force
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20
Q

Under what circumstance is 1 joule of work done?

A
  • when a force of 1 newton causes a displacement of 1 metre
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21
Q

How many N/m are equal to 1 joule of energy

A

1 Nm = 1J

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22
Q

What occurs when work is done against frictional forces?

A
  • a rise in temperature of the object occurs
  • kinetic energy is converted to heat
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23
Q

Why does air resistance slow down a projectile?

A
  • the object does work against the air resistance
  • kinetic energy is converted in to heat, slowing down the object
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24
Q

Explain the relationship between the force applied and the extension of an elastic object - Hooke’s Law

A

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

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25
Q

What is meant by an inelastic deformation?

A
  • A deformation which results in the object being permanently stretched
  • the object doesn’t return to its original shape when the force is removed
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26
Q

State the equation relating force, spring constant and extension . Give appropriate units.

A

Force= Spring Constant x Extension
Force: N
spring constant : N/m
Extension : m

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27
Q

What type of energy is stored in a spring when it is stretched?

A

Elastic potential energy

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28
Q

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

A

Compression

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29
Q

When work is done to stretch a spring,
how much elastic potential energy is
stored?

A

Provided that the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal

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30
Q

Define moment.

A

The turning effect of a force around a
point/pivot

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31
Q

State the equation for
moment of a force and the units

A

Moment = force x distance
moment: Newton metre (Nm)
force: Newton
distance: metre

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32
Q

What distance measurement is used when calculating a moment?

A
  • the perpendicular distance from the pivot to the line of action of the force
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33
Q

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

A

The sum of the clockwise moment about the pivot is equal to the sum of the anticlockwise moment about the pivot

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34
Q

State two ways to increase the size of a moment

A
  • Increase the size of the applied force
  • Increase the perpendicular distance
    from the line of action of the force to
    the pivot
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35
Q

What three parts make up a lever system?

A
  1. Load
  2. Effort
  3. Pivot
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36
Q

Explain how a lever can act
as a force multiplier

A
  • if the distance between the effort and the pivot is greater than the distance between the pivot and load, the force applied o the load is greater than the effort force.
  • this is since the moment on both the effort and load must be the same
  • ( less force is needed to get the same moment )
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37
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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38
Q

What determines the moment of a gear wheel?

A

the size of the wheel

39
Q

Describe what a gear is and
what function it serves in
machinery

A
  • A gear is a circular disc with teeth. In
    machinery it is interlocked with other gears
  • in order to transmit the rotational effects of a force from one place to another
40
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 will also produce a larger moment
41
Q

What is meant by the term ‘ fluid’ ?

A

a liquid or a gas

42
Q

In any fluid, at what angle do the forces due to pressure act on a given surface

A
  • at right angles ( normal to) the surface
43
Q

State the equation used to calculate pressure. Give appropriate units

A

Pressure = force / area
pressure: Pascals
Force: Newtons
Area: Metre”2

44
Q

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

A

the atmosphere becomes less dense as altitude increases.

45
Q

Explain why atmospheric pressure decreases with an increase in height.

A
  • Pressure is created by collisions of air molecules
  • the quantity of molecules ( and so weight) decreases as the height increases
  • this means atmospheric pressure decreases with an increase of height
46
Q

What is the Earth’s atmosphere?

A
  • a thin ( relative to the magnitude of the Earth) layer of gas surrounding of the Earth
47
Q

How does pressure in fluids increase with depth?

A
  • As depth increases, the mass of liquid above the object also increases
  • This means that the force due to the mass increases
  • Since the force has increased whilst the area has remained constant, the pressure will increase
48
Q

Describe and explain how
the pressure exerted by a liquid
on an object changes with
increasing depth

A

● As depth increases there is more liquid
above the object
● This increases the weight of the liquid
particles acting on the object
● As a result, pressure increases

49
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 increases
  • The weight of the fluid is greater. This means that the force from the fluid above a certain point is larger.
  • Since the force has increased, the pressure also increases
50
Q

Which equation shows the magnitude of pressure in liquids at different depths?

A

Pressure due to a column of liquid ( Pa ) = Column height (m) x density ( kg/m”3) x gravitational field strength (N/kg)
P=hpg

51
Q

why are objects in a fluid subject to an upthrust?

A
  • When the pressure exerted by the liquid at the bottom of an object is greater than the pressure exerted at the top of an object.
  • This creates a resultant force upwards (upthrust)
52
Q

What is upthrust always equal to?

A
  • the weight of the fluid that the object displaces
53
Q

Give thee factors which influence whether an object will sink or float?

A
  • upthrust
  • weight
  • density of fluid
54
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 displaced fluid.
  • 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.
55
Q

How is atmospheric
pressure created on a surface?

A

When air molecules collide with a surface

56
Q

Explain why atmospheric
pressure changes with altitude

A

Air molecules colliding with a surface
creates atmospheric pressure
● At increasing altitude, there are fewer
molecules of air above a surface so the
number of collisions between the air
molecules and the surface decreases
● As altitude increases, the weight of air
above the surface will decrease so
pressure will decrease

57
Q

State a typical value for :
- human walking speed
- human running speed
- human cycling speed
- train speed
- plane speed

A

a. 1.5 m/s
b. 3 m/s
c. 6 m/s
d. 100 km/h
e. 900 km/h

58
Q

State the equation linking distance , speed and time. Give appropriate units

A

distance = speed x time
distance : m
speed: m/s
time: s

59
Q

why can object travelling at a constant speed in a circle not have a constant velocity

A
  • speed is a scalar quantity
  • velocity is a vector quantity which means it can only be constant if the direction is constant
  • in circular motion, the direction is continuously changing
60
Q

What piece of equipment can be used
to measure distance

A

Ruler, trundle-wheel

61
Q

What piece of equipment can be used
to measure time?

A

Stop watch, light gates

62
Q

. How can speed be calculated from a
distance-time graph?

A

the gradient

63
Q

How can the speed of an accelerating
object be found from a distance-time
graph at a particular time?

A

Draw a tangent to the curve at that time and
find the gradient of the tangent.

64
Q

What is the word and symbol equation for
acceleration?

A

Acceleration = change in velocity/time taken
a= v/t
units: m/s”2

65
Q

How can acceleration be determined
from a velocity-time graph?

A

The gradient of a velocity-time graph.

66
Q

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

A
  • it is equal to the area under the graph
67
Q

What is the acceleration of objects near the Earth’s surface falling freely under gravity?

A

9.8 m/s2

68
Q

. What is terminal velocity?

A
  • An object falling through a fluid initially accelerates due to the force of gravity.
  • air resistance will slowly equal weight and
  • The resultant force will be zero and the object will move at its terminal velocity.
69
Q

State Newton’s First Law:

A
  • An object at rest will remain at rest and a
    moving object will continue moving at constant velocity as long as no resultant force acts on the object
70
Q

What is needed for velocity of an
object to change?

A

An unbalanced/resultant force

71
Q

. What is inertia?

A

The tendency of objects to continue in their
state of rest or of uniform motion is called
inertia

72
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
73
Q

State Newton’s Second Law:

A

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the
object.

74
Q

What is the word equation for
Newton’s Second Law?

A

Resultant force = mass x acceleration

75
Q

. What is inertial mass?

A

A measure of how difficult it is to change the
velocity of an object. It is defined as the ratio of force over acceleration.

76
Q

. State Newton’s Third Law

A

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

77
Q

What is the stopping distance of a
vehicle?

A
  • It is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance)
78
Q

For a given braking distance, if the vehicle’s so speed is increased what can be said about its stopping distance

A

For a given braking force the greater the speed of the vehicle, the greater the stopping
distance.

79
Q

What is a typical human reaction time?

A

0.2 - 0.9 s

80
Q

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

A

Fatigue
drugs
alcohol

81
Q

Give two factors which affect braking distance

A
  • adverse road and weather conditions (such as wet and icy)
  • poor condition of the vehicle (such as the brakes and tyres)
82
Q

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

A
  • When a force is applied to the brakes of a
    vehicle
  • work done by the friction force
    between the brakes
  • kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs
  • temperature of brakes increases
83
Q

In order to stop a vehicle within a
certain distance, how does the speed
of the vehicle affect the necessary
braking force

A

The greater the speed of a vehicle the greater
the braking force needed to stop the vehicle in a certain distance

84
Q

What are the dangers of large braking
forces needed to slow down fast
moving vehicles?

A
  • The greater the braking force the greater the deceleration of the vehicle.
  • Large decelerations may lead to brakes overheating and/or loss of control.
85
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
86
Q

State the equation used to calculate an object’s momentum.

A

momentum = mass x velocity

87
Q

What is the unit used for momentum?

A
  • kg m/s
  • kilogram metres per seconds
88
Q

. What is the principle of conservation
of momentum?

A

In a closed system, the total momentum before an event is equal to the total momentum after the event.

89
Q

State an equation linking change in momentum, force and time.

A

Force= change in momentum / time

90
Q

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

A

the rate of change of momentum

91
Q

If an object’s change in momentum is fixed, what is the only way to reduce the force that the object experiences ?

A
  • increase the length of time over which the change of momentum occurs
92
Q

Explain how a crumple zone
protects a driver in a crash?

A
  • Increases time for driver to stop
  • Decreases the rate of change of
    momentum
  • Reduces force on driver
93
Q

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

A
  • passenger must decelerate from the vehicles velocity at impact to zero, meaning they undergo a fixed change of momentum
  • the force they experience is equal to rate of change of momentum
  • seatbelt increases time over which force is applied
  • reducing the rate of change of momentum

[GCSE] physics (9 decks)

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