Physics ✿ forces

what should happen in order to cause an object to stretch, bend or compress?

2 forces must act on the object

the extension of an elastic object is _______ proportional to the force applied

directly

Hooke’s law

the extension of an elastic object is directly proportional to the force applied

directly proportional

when one variable changes, the other one changes by same amount

limit of proportionality

the length a spring can be stretched before it can no longer return to its original length

elastic deformation

when a spring is stretched and can return to its original length

inelastic deformation

when a spring is stretched and cannot return to its original length

distance

a scalar quantity that measures how far an object moves

displacement

a vector quantity that measures how far out of place place A is from place B

velocity

speed in a given direction

acceleration

the rate of change of velocity

equation for acceleration (on a graph)

change in velocity / time taken

what does this graph show?

constant velocity

what does this graph show?

constant acceleration

terminal velocity

what is it caused by?

the maximum speed objects reach when falling

air resistance

how do you find the speed on a distance time graph?

change is y values / change in x values

if an object is moving in a circular motion, what happens to the velocity?

it is always changing and is perpendicular to the acceleration

what is the typical speed of a person walking?

1.5m/s

what is the typical speed of a person running?

3m/s

what is the typical speed of a person cycling?

6m/s

what is the typical speed of a car?

25m/s

what is the typical speed of a train?

30m/s

what is the typical speed of a plane?

250m/s

what happens to terminal velocity when an object has..

• a large surface area?

• a small surface area?

and why?

large surface area:

• has a lower terminal velocity as more air resistance acts on it

small surface area:

• has a higher terminal velocity as less air resistance acts on it

uniform acceleration

when an object's speed is increasing at a constant rate

briefly describe an experiment you could do to compare people’s reaction times

• have a person sit with their hand open ready to catch a ruler

• hold the ruler vertically with the 0 cm aligned with the top of the person’s finger

• drop the ruler

• record the measurement at the point where the ruler was caught

state how a person with a parachute enters terminal velocity [3]

• weight makes person accelerate downwards

• acceleration causes air resistance to increase until it reaches same size as weight

• this causes person to fall at constant speed (terminal velocity)

state how a person with a parachute can land safely [3]

• opening parachute increases surface area making air resistance greater than weight

• resultant force upwards causes deceleration

• air resistance decreases until it balances the weight (slow terminal velocity)

newtons first law

objects will stay at rest or move at constant speed unless a net resultant force is acted on it

newtons second law

the acceleration is proportional to the resultant force

and inversely proportional to the object’s mass

newtons third law

whenever 2 objects interact the forces they exert on each other are equal but opposite

give an example of newtons third law in action

a bird flying →

• bird’s wings push downwards

• air pushes upwards on bird

• bird flies up

stopping distance

thinking distance + braking distance

what is the typical driver’s reaction time?

0.2 - 0.9 seconds

state 3 factors affecting reaction time

• drugs/ alcohol

• distractions e.g. animals

• tiredness

state 4 factors affecting braking distance

• wet or icy roads

• poor vehicle condition

• fast speed of vehicle

• friction from brake and wheel reduced kinetic energy

momentum

a measure of how difficult it is to stop a moving object

conservation of momentum

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

closed system

no external forces

scalar

a quantity that has a magnitude only

vector

a quantity that has a magnitude and direction which is usually represented as an arrow

name 2 forces

push and pull

non contact forces

a force made when objects are physically separated

contact forces

a force made when objects are physically touching

what are forces measured in?

newtons (N)

the weight and mass of an object are __________ proportional

directly

what is the difference between mass and weight?

mass → amount of matter in an object

weight → force of gravity acting on an object

what happens to an object if forces are balanced?

the resultant force is zero

the object stays at rest or moves at constant speed

resultant force

overall force on an object

when a force causes an object to move through a distance, ______ is _______ on the object

work is done

1 newton meter =

1 joule

work done against friction

when an object is moved along a rough surface

what does work done against friction produce?

heat (thermal energy)

equation for work done

force applied (n) x distance (m)

mechanical work

a force which causes an object to move

transferring energy to the kinetic energy store of the object

gravitational work

a force which lifts up an object

transferring energy to the gravitational potential store of the object

vectors

a quantity that has a magnitude and a direction

scalars

quantities that only have a magnitude