P1-Topic 5-Forces 2022 Flashcards
What is a scalar quantity?
has magnitude only
What is a vector quantity?
have magnitude and an associated direction
How can a vector quantity be drawn and
what does it show?3
As an arrow
length of the arrow represents the magnitude
arrow points in the associated direction
What is a force?1
a push or pull that acts on an object due to the interaction
with another object
Give three examples of contact forces
- Friction
- Air resistance
- Tension
Give three examples of non-contact
forces
- Gravitational forces
- Electrostatic forces
- Magnetic forces
Give three examples of vector quantities
Velocity
- Displacement
- Force
Give three examples of scalar quantities.
Temperature ● Time ● Mass ● Speed ● Distance ● Energy temperature
What is meant by an object’s centre of mass?
The single point where an object’s
weight can be considered to act through.
What piece of equipment can be used to measure an
object’s weight?
A calibrated spring-balance or newtonmeter
What is the name given to the single force that is equivalent to all the other forces acting on a given object?
resultant force
What is the equation used to calculate
work done? Give appropriate units
Work done = Force x Distance
Work done (Joules), Force (Newtons), Distance (metres)
What distance must be used when calculating work
done?
must be the distance that is moved
along the line of action of the force
Under what circumstance is 1 joule of work done?
When a force of 1 Newton causes a
displacement of 1 metre.
How many Newton-metres are equal to 1 joule of
energy?
1 Nm = 1 J
What occurs when work is done against frictional
forces?2
A rise in temperature of the object
occurs
Kinetic energy is converted to heat
Why does air resistance slow down a projectile?2
The object does work against the air
resistance
Kinetic energy is converted in to heat,
slowing down the object
What is weight? and unit of measure
The force that acts on an object due to
gravity and the object’s mass
in newtons (N)
What quantities does weight depend on?
Weight = mass x gravitational field strength
● The object’s mass
● The gravitational field strength at the
given position in the field
Explain the relationship between the
force applied and the extension of an
elastic object Hooke’s law
The extension is directly proportional to
the force applied, provided that the limit
of proportionality is not exceeded.
What is meant by an inelastic (plastic)
deformation?2
● 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
State the equation relating force, spring constant and extension. Give appropriate units
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
what is elastic deformation 2
The object returns to its original shape when the load has been removed
o Elastic band
What can extension be replaced with in
the equation for spring force?
Compression
difference between a linear and non-linear relationship between force and extension 4
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
what happens if a graph is just linear
If graph is just linear, with no non-linear end section, the material is brittle, so snaps instead of stretches after the elastic limit
What is meant by an object’s centre of mass?
The single point where an object’s
weight can be considered to act through
What piece of equipment can be used to measure an
object’s weight? 2
A calibrated spring-balance or newtonmeter
What is meant by the term ‘fluid’?
A liquid or a gas
In any fluid, at what angle do the forces
due to pressure act on a given surface?
At right angles (normal to) the surface
State the equation used to calculate
pressure. Give appropriate units
Pressure = Force/Area
Pressure (Pascals), Force (Newtons),
Area (metre²)
What happens to the density of the
atmosphere with increasing altitude?
The atmosphere becomes less dense as
altitude increases
Explain why atmospheric pressure
decreases with an increase in height3
● 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
What is the Earth’s atmosphere?
A thin (relative to the magnitude of the
Earth) layer of gas surrounding the
Earth.
How does pressure in fluids increase
with depth?3
use equation p=F/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.
Why does pressure in fluids increase
with density?4
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.
What equation shows the magnitude of pressure
in liquids at different depths?
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
Why are objects in a fluid subject to an
upthrust?3
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.
What is upthrust always equal to?
The weight of the fluid that the object
displaces.
What factors influence whether an object
will sink or float?
● Upthrust
● Weight
● Density of fluid
Explain why an object with a density
greater than that of water can never
float 3
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.
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
● The object has zero displacement
● Displacement is a vector quantity so it also
involves direction
● The object starts and ends at the same point
what is the typical value for the speed of sound, walking running and cycling 4
sound = 330m/s
walking ̴ 1.5 m/s
running ̴ 3 m/s
cycling ̴ 6 m/s
State the equation linking distance,
speed and time. Give appropriate units
Distance = Speed x Time
Distance (m), Speed (m/s), Time (s)
s=vt (physics)
Why can an object travelling at a constant speed in a
circle not have a constant velocity? (Higher) 3
● 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
How can speed be calculated from a
distance-time graph?
The speed is equal to the gradient of the
graph by drawing a tangent
State the equation for the average acceleration of an
object. Give appropriate units
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
How to calculate acceleration and distance traveled in a velocity- time graph 2
Gradient is acceleration
Sharper gradient means greater acceleration
- Negative gradient is deceleration
- Horizontal line means constant speed
Area under line = distance traveled
Give an approximate value for the acceleration of an
object in free fall under gravity near the Earth’s
surface.
9.8 m/s²
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
equation for velocity using acceleration
(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
State the equation used to calculate an object’s momentum
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
In a closed system, what can be said
about the momentum before and after a
collision?2
The total momentum before is equal to
the total momentum afterwards
conservation of momentum
State an equation linking change in momentum,force and time
Force x Time = Change in Momentum
F Δt = mΔv
What quantity is equal to the force experienced in a collision?
The rate of change of momentum
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
Explain how a seatbelt improves a
passenger’s safety during a collision. 4
● 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
