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Physics > Unit 5 - Forces > Flashcards

Unit 5 - Forces Flashcards

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1
Q

What is a scalar quantity?

A

● A quantity that only has a magnitude
● A quantity that isn’t direction
dependent

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and
an associated direction.

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3
Q

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

A

● As an arrow
● The length of the arrow represents the
magnitude
● The arrow points in the associated
direction

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4
Q

What is a force?

A

A push or pull acting on an object due to
an interaction with another object.

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5
Q

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

A
  1. Contact forces (objects touching)
  2. Non-contact forces (objects separated)
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6
Q

Give three examples of contact forces.

A
  1. Friction
  2. Air resistance
  3. Tension
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7
Q

Give three examples of non-contact
forces

A
  1. Gravitational forces
  2. Electrostatic forces
  3. Magnetic forces
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8
Q

Is force a vector or a scalar quantity?

A

● Vector
● It has both a magnitude and an
associated direction

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9
Q

Give three examples of vector quantities.

A
  1. Velocity
  2. Displacement
  3. Force
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10
Q

Give three examples of scalar quantities.

A

● Temperature
● Time
● Mass
● Speed
● Distance
● Energy

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11
Q

What is weight?

A

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

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12
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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13
Q

What is the unit used for weight?

A

The Newton (N).

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14
Q

What is the unit used for gravitational
field strength?

A

N/kg

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15
Q

What is 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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16
Q

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

A

A calibrated spring-balance or newton-meter.

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17
Q

What is the name given to the single
force that is equivalent to all the other
forces acting on a given object?

A

The resultant force.

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18
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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19
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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20
Q

What 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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21
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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22
Q

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

A

1 Nm = 1 J

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23
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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24
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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25
Explain the relationship between the force applied and the extension of an elastic object
The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
26
What is meant by an inelastic (plastic) deformation?
● A deformation which results in the object being permanently stretched ● The object doesn’t return to its original shape when the force is removed
27
What type of energy is stored in a spring when it is stretched?
Elastic potential energy.
28
What can extension be replaced with in the equation for spring force?
Compression.
29
Does a distance quantity require a specific direction? i.e. Is it a scalar or vector quantity?
No specific direction is required so it is a scalar quantity.
30
If an object moves 3 metres to the left and then 3 metres back to its initial position, what is the object’s total displacement?
● The object has zero displacement ● Displacement is a vector quantity so it also involves direction ● The object starts and ends at the same point
31
State a typical value for the speed of sound.
330 m/s
32
What is a typical value for human walking speed?
1.5 m/s
33
What is a typical value for human running speed?
3 m/s
34
What is a typical value for human cycling speed?
6 m/s
35
State the equation linking distance, speed and time. Give appropriate units.
Distance = Speed x Time Distance (m), Speed (m/s), Time (s)
36
Why can an object travelling at a constant speed in a circle not have a constant velocity?
● 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
37
How can speed be calculated from a distance-time graph?
The speed is equal to the gradient of the graph.
38
What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
● Drawing a tangent to the curve at the required time ● Calculating the gradient of the tangent
39
State the equation for the average acceleration of an object. Give appropriate units
Acceleration = (Change in Velocity)/(Time Taken) Acceleration (m/s²), Velocity (m/s), Time (s)
40
How can the distance travelled by an object be calculated from a velocity-time graph?
It is equal to the area under the graph.
41
Give an approximate value for the acceleration of an object in free fall under gravity near the Earth’s surface
9.8 m/s²
42
What can be said about the resultant force acting on an object when it is falling at terminal velocity?
● The resultant force is zero ● When at terminal velocity, the object is moving at a constant speed and so isn’t accelerating
43
State Newton’s first law for a stationary object.
If the resultant force on a stationary object is zero, the object will remain at rest.
44
State Newton’s first law for a moving object.
If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).
45
What can be said about the braking forces and driving forces when a car is travelling at constant velocity?
The braking forces are equal to the driving forces.
46
If an object changes direction but remains at a constant speed, is there a resultant force?
Since there is a change in direction, there is a change in velocity and so there must be a resultant force.
47
What is inertia?
The tendency of an object to continue in its state of rest or uniform motion.
48
State the defining equation for Newton’s Second Law
Resultant force = Mass x Acceleration F = ma
49
State Newton’s Second Law in words
An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.
50
What is inertial mass?
● A measure of how difficult it is to change a given object’s velocity ● The ratio of force over acceleration
51
What is the symbol used to represent an approximate value?
≈
52
State Newton’s Third Law.
Whenever two objects interact, the forces that they exert on each other are always equal and opposite.
53
What is the stopping distance of a vehicle equal to?
The sum of thinking distance and braking distance.
54
For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?
The stopping distance is increased with an increase in speed.
55
Give a typical range of values for human reaction time.
0.2 seconds - 0.9 seconds
56
Give three factors which can affect a driver’s reaction time.
1. Tiredness 2. Drugs 3. Alcohol
57
Give two factors which may affect braking distance.
1. Adverse (wet/icy) road conditions 2. Poor tyre/brake conditions
58
Describe the energy transfers that take place when a car applies its brakes.
● 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
59
To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?
The braking force must also be increased.
60
State two consequences of a vehicle undergoing very large decelerations.
1. Kinetic energy converted to heat is very high causing brakes to overheat 2. Loss of control of the vehicle
61
State the equation used to calculate an object’s momentum.
Momentum = Mass x Velocity
62
What is the unit used for momentum?
kg m/s kilogram metres per seconds
63
In a closed system, what can be said about the momentum before and after a collision?
The total momentum before is equal to the total momentum afterwards
64
State an equation linking change in momentum, force and time.
Force x Time = Change in Momentum F Δt = mΔv
65
What quantity is equal to the force experienced in a collision?
The rate of change of momentum.
66
If an object’s change of momentum is fixed, what is the only way to reduce the force that the object experiences?
Increase the length of time over which the change of momentum occurs.
67
Explain how a seatbelt improves a passenger’s safety during a collision.
● Passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum ● The force they experience is equal to the rate of change of momentum ● Seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced

Physics (7 decks)

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