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Physics > P1-Topic 5-Forces 2022 > Flashcards

P1-Topic 5-Forces 2022 Flashcards

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1
Q

What is a scalar quantity?

A

has magnitude only

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2
Q

What is a vector quantity?

A

have magnitude and an associated direction

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3
Q

How can a vector quantity be drawn and

what does it show?3

A

As an arrow

length of the arrow represents the magnitude

arrow points in the associated direction

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4
Q

What is a force?1

A

a push or pull that acts on an object due to the interaction

with another object

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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

Velocity

  1. Displacement
  2. Force
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8
Q

Give three examples of scalar quantities.

A 
Temperature
● Time
● Mass
● Speed
● Distance
● Energy 
temperature
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9
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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10
Q

What piece of equipment can be used to measure an

object’s weight?

A

A calibrated spring-balance or newtonmeter

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11
Q

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

A

resultant force

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12
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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13
Q

What distance must be used when calculating work

done?

A

must be the distance that is moved

along the line of action of the force

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14
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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15
Q

How many Newton-metres are equal to 1 joule of

energy?

A

1 Nm = 1 J

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16
Q

What occurs when work is done against frictional

forces?2

A

A rise in temperature of the object
occurs

Kinetic energy is converted to heat

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17
Q

Why does air resistance slow down a projectile?2

A

The object does work against the air
resistance

Kinetic energy is converted in to heat,
slowing down the object

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18
Q

What is weight? and unit of measure

A

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

in newtons (N)

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19
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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20
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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21
Q

What is meant by an inelastic (plastic)

deformation?2

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

A spring when pulled too far

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22
Q

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

A 
f force = s pring constant × extension
 F  = k e 
force, F, in newtons, N
spring constant, k, in newtons per metre, N/m
extension, e, in metres, m
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23
Q

what is elastic deformation 2

A

The object returns to its original shape when the load has been removed
o Elastic band

24
Q

What can extension be replaced with in

the equation for spring force?

A

Compression

25
Q

difference between a linear and non-linear relationship between force and extension 4

A

Linear line :
- This is elastic region
following Hooke’s Law
• The point it stops being linear is the limit of proportionality.
- From then on, it does not obey Hooke’s Law

Non-Linear line
- There is plastic behaviour 
- It is not following Hooke’s Law
- If shallow
o Lots of extension for not a lot of force
o Easy to stretch
26
Q

what happens if a graph is just linear

A

If graph is just linear, with no non-linear end section, the material is brittle, so snaps instead of stretches after the elastic limit

27
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

28
Q

What piece of equipment can be used to measure an

object’s weight? 2

A

A calibrated spring-balance or newtonmeter

29
Q

What is meant by the term ‘fluid’?

A

A liquid or a gas

30
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

31
Q

State the equation used to calculate

pressure. Give appropriate units

A

Pressure = Force/Area
Pressure (Pascals), Force (Newtons),
Area (metre²)

32
Q

What happens to the density of the

atmosphere with increasing altitude?

A

The atmosphere becomes less dense as

altitude increases

33
Q

Explain why atmospheric pressure

decreases with an increase in height3

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

34
Q

What is the Earth’s atmosphere?

A

A thin (relative to the magnitude of the
Earth) layer of gas surrounding the
Earth.

35
Q

How does pressure in fluids increase
with depth?3
use equation p=F/A

A

As the depth increases, the mass of liquid
above that depth 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.

36
Q

Why does pressure in fluids increase

with density?4

A

As the density of a fluid increases, the number of
particles in a given volume increases.

Consequently 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.

37
Q

What equation shows the magnitude of pressure

in liquids at different depths?

A

pressure = height of the column × density of the liquid
× gravitational field strength

[ p = h ρ g ]
pressure, p, in pascals, Pa
height of the column, h, in metres, m
density, ρ, in kilograms per metre cubed, kg/m3
gravitational field strength, g, in newtons per kilogram, N/kg

38
Q

Why are objects in a fluid subject to an

upthrust?3

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 on whether the
upthrust is more or less than your weight.

39
Q

What is upthrust always equal to?

A

The weight of the fluid that the object

displaces.

40
Q

What factors influence whether an object

will sink or float?

A

● Upthrust
● Weight
● Density of fluid

41
Q

Explain why an object with a density
greater than that of water can never
float 3

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.

42
Q

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? 3

A

● The object has zero displacement
● Displacement is a vector quantity so it also
involves direction
● The object starts and ends at the same point

43
Q

what is the typical value for the speed of sound, walking running and cycling 4

A

sound = 330m/s
walking ̴ 1.5 m/s
running ̴ 3 m/s
cycling ̴ 6 m/s

44
Q

State the equation linking distance,

speed and time. Give appropriate units

A

Distance = Speed x Time
Distance (m), Speed (m/s), Time (s)

s=vt (physics)

45
Q

Why can an object travelling at a constant speed in a

circle not have a constant velocity? (Higher) 3

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

46
Q

How can speed be calculated from a

distance-time graph?

A

The speed is equal to the gradient of the

graph by drawing a tangent

47
Q

State the equation for the average acceleration of an

object. Give appropriate units

A

acceleration = change in velocity
time taken
a =∆ v/t
acceleration, a, in metres per second squared, m/s2
change in velocity, ∆v, in metres per second, m/s
time, t, in seconds, s

48
Q

How to calculate acceleration and distance traveled in a velocity- time graph 2

A

Gradient is acceleration
Sharper gradient means greater acceleration
- Negative gradient is deceleration
- Horizontal line means constant speed

Area under line = distance traveled

49
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/s²

50
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 zero
● When at terminal velocity, the object is
moving at a constant speed and so
isn’t accelerating

51
Q

equation for velocity using acceleration

A

(final velocity)² − (initial velocity)²
= 2 × acceleration × distance
v² − u²= 2 a s
final velocity, v, in metres per second, m/s
initial velocity, u, m/s
acceleration, a, in metres per second squared, m/s2
distance, s, in metres, m

52
Q

State the equation used to calculate an object’s momentum

A 
momentum = mass × velocity
p  = m v
momentum, p, in kilograms metre per second, kg m/s
mass, m, in kilograms, kg
velocity, v, in metres per second, m/s
53
Q

In a closed system, what can be said
about the momentum before and after a
collision?2

A

The total momentum before is equal to
the total momentum afterwards

conservation of momentum

54
Q

State an equation linking change in momentum,force and time

A

Force x Time = Change in Momentum

F Δt = mΔv

55
Q

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

A

The rate of change of momentum

56
Q

If an object’s change of 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

57
Q

Explain how a seatbelt improves a

passenger’s safety during a collision. 4

A

● 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 (10 decks)

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