P8 + P9

Upthrust Definition

upward force exerted on an object in a fluid

Friction definition

resistive force due to 2 objects in contact

Air resistance definition

resistive force due to moving through air

Weight definition + unit

downwards force due to gravity, unit newton

Lift definition

force that uses motion to make an object rise up

What are scalar quantities?

Physical objects that have magnitude (size) but no specific direction

examples of magnitude

length (cm), mass (kg)

Examples of scalar quantities 5

distance, speed, temperature, time, mass

What are vector quantities

Physical quantities that have magnitude and direction

Example vector quantities 5

displacement, velocity, force, momentum, acceleration

What do each aspects of an arrow represent for vector quantites

direction of arrow: direction of vector quantity, length of arrow: magnitude of vector quantity

Displacement definition

how far you have travelled from one point to another in a straight line

Distance definition

the total distance travelled

is speed a scalar or vector quantity?

scalar quantity

Speed definition

measure of the distance travelled in a given time, how fast an object moves

Velocity definition

measure of the displacement of an object in a given time

What is a free body diagram

a diagram used to show relative magnitude + direction of all forces acting upon an object in a given situation

What is the object represented as in a free body diagram

A dot

Free body diagram/scale diagram

Force definition

a quantity that when applied will change the motion/shape of an object

What can forces do to an object?

change speed, change shape, change direction

What are the 3 main types of forces?

push, pull, twist

Contact force definition

2 objects have to be touching for a force to act

non-contact force definition

object don't need to be touching for the force to act

Example of contact forces 5

water resistance, friction, air resistance, lift, normal contact force

Example of non-contact forces 3

gravitational force, magnetic force, electrostatic force

What is Newton's Third Law

when 2 objects interact, they exert an equal and opposite force on each other

Resultant force definition

The single force you will get if you added all the forces acting on an object together, a single force that has the same effect as all the forces acting on an object

What does it mean if the resultant force is 0

the forces are balanced or the object stays at rest or same/constant speed + direction

How will the object change if the resultant force is above 0?

speed or direction of object will change

How to calculate the resultant force of 2 forces affecting an object in the same direction?

Sum the forces

How to calculate the resultant force of two forces going in opposite directions on an object?

the difference of the forces

Moments defnition

the turning effect of a force (the moment of the force)

what is the pivot

the axis of rotation

How to change the size of a moment

change the perpendicular distance from pivot, change the size of the force (weight), if you increase these then you get a bigger moment

Moment equation with units

Moment (Nm) = force (N) x perpendicular distance from pivot(m) M = Fd

Levers definition

A simple machine which is designed to help lift an object

What is a force multiplier and give an example

Something that exerts a greater force than the force applied to it by effort e.g. lever

load definition

the object you're lifting

effort definiton

force you apply on load

Lever diagram

What does a gear do?

it changes the moment of a turning effect

What happens when you turn a gear (with a connecting one)?

Turning force applied to one wheel --> interlocking wheel turns adjacent wheel in opposite direction

What do the teeth on gears do?

The teeth prevent slipping

What does a larger gear mean?

a slower rotation but larger moment

What does a smaller gear mean?

A faster rotation but smaller moment

What should you do to increase the moment of a turning effect using gears?

smaller gear wheel needs to drive a larger gear wheel

Moments ratio formula

ratio of moments = ratio of teeth = ratio of radii

Ratio moment formula but written out

moment A/moment B = teeth of A/teeth of B = radius of A/radius of B

Gravitational field definition

area around an object where another body experiences a force

Which objects have a gravitational field around them?

All of them

How does the size of an object affect the gravitational field?

The bigger the object, the bigger the gravitational field

Why is there weight (the force)?

The force is due to gravitational field around earth

Mass definition

how much material is in an object and is fixed

Mass description + units

Doesn't change wherever you go, kg

Centre of mass definition

The single point of an object where all the weight is considered to act through

Relationship between weight and mass?

Weight is directly proportional to mass

Weight equation

weight = mass x gravitational field strength, W = mg, newtons, kg, N/kg

Where is the centre of mass of a uniform ruler?

the midpoint

Where is the centre of mass of a symmetrical object?

along the axis of symmetery

What happens to an object when freely suspended?

it comes to rest with its centre of mass directly underneath the point of suspension

How to find the centre of mass of an irregular shape (not required practical)

1. Put a hole in one corner of the card and suspend the card from a rod

2. Use a plumb line to draw a vertical line on the card from the rod

3. Repeat the procedure, hanging the card from a different corner

When is equilibrium in moments terms + resultant force

If clockwise + anticlockwise moments are equal, the system is at equilibrium and resultant force is 0

What is the principle of moments?

Sum of all clockwise moments about any pivot = the sum of all anticlockwise moments about any pivot

Speed formula

distance/time = speed

speed of walking

1.5 m/s

speed of running

3 m/s

speed of cycling

6 m/s

speed of sound in air

330 m/s

Describe a distance time graph of a stationary object

Horizontal line

Describe a distance time graph of an object moving at a constant speed

Diagonal straight line

Describe a distance time graph of an object moving accelerating

Exponential curve upwards

How to calculate the speed using a distance time graph of an object moving at a constant speed

Find the gradient of the line: change in y/change in x

How to calculate the average speed

total change in y/total change in x

How to calculate the speed of an accelerating object

draw a tangent at the point you want to know the speed + find the gradient of the tangent

Acceleration definition

the rate of change of velocity with respect to time

Describe acceleration in motion of an object and resultant force terms

If the motion of an object is going in the same direction of the resultant force: acceleration

Describe deceleration in motion of an object and resultant force terms

If the motion of an object is going in the opposite direction of the resultant force: deceleration

If the resultant force is 0, what happens to an object if it is stationary

It remains stationary

If the resultant force is 0, what happens to an object if it is moving

It will move at a constant velocity

Describe a velocity time graph of an object with constant velocity

Flat straight line

Describe a velocity time graph of an object with constant acceleration

Diagonal straight line upwards

Describe a velocity time graph of an object with constant deceleration

Diagonal straight line downwards

Acceleration formula

(final velocity - initial velocity) / time taken

Units of acceleration, velocities and time taken in acceleration formula

Acceleration: m/s^2, Final + initial velocities: m/s, Time taken: s

If question asks for acceleration and the overall value is deceleration?

answer negative

If question asks for deceleration and the answer is decelerating?

answer positive

2nd acceleration formula (more indirect one)

(final velocity)^2 - (initial velocity)^2 = 2 x acceleration x distance

How to calculate the acceleration of an object using a velocity-time graph?

Gradient of velocity-time graph line

Freely suspended definition

object returns to its equilibrium position when the turning force is removed

How do force multipliers work?

Effort acts further from fulcrum than force of force multiplier on ___ therefore force of force multiplier > effort