physics - toppic 5 forces and motion Hookes law + Forces and motion using F=ma

scalar

what does it tell us

how are they represented

examples

scalars tell us a magnitude (an amount) of something

tgey are represented by numbers è.g 20 m/s

È.G mass, distance, time, speed

vector

what does it tell us

how are they represented

examples

vectors tell us BOTH the magnitude and direction of something

vectors are represented by numbers and arrows

e.g velocity, acceleration

distance define

ghe distance is something travels us how far it actually goes

displacement define

the displacement ment is how far away something ends up from it’s starting position

equation linking distance, speed and time

Speed(m/s) = distance(m) / time(s)

acceleration define

when things are getting faster or a change in direction

deceleration

is when things get closer

equation linking acceleration, change jn speed and time

acceleration(m) = change in speed(m/s²) / time(s)

other acceleration equation tgat cannot be put in an equation triangle

(final velocity)² - (initial velocity)² = 2 X acceleration X distance

V² - U² = 2 AD

how do you work out … from the acceleration equation

final velocity

distance

initial velocity

V² - U² = 2 AD

V = square root 2AD + U²

D = V² - U² / 2A

U = square root V² - 2AD

displacement time graphs

constant speed

acceleration

stationary

displacement

displacement = whrn goes down it goes to starting point

displacement time graphs

gradient

is the speed

speed = gradient = change in y (distance) / change in x (time)

displacement time graphs

instantaneous speed

• if the graph shows a curved line (accelerating) draw tangent at point on curve

• gradient of tangent = instantaneous speed

Velocity - time graphs

constant speed

velocity increasing / accelerating

gradient (acceleration)

• gradient (acceleration) = change jn y (speed) / change in x (time taken)

force define

a push or a pull that acts on an object (because of an interaction with another object)

define contact force

a force where objects are physically touching e.g air resistance, normal, friction

non contact force define

a force where objects arent physically touching e.g gravity, weight, magnets

define friction

where the contact between two objects resists movement

example of a contact force

define air resistance

where the air particles hitting the object slow down a falling object

a type of contact force

define weight

fall due to the force of gravity

type of non contact force

define magnets

magnets attract objects with magnetic force

type of non contact force

define mass

the amount of matter something contains, measured in kf

mass of an object doesn’t depend on anything else. It is constant

define weight

the force of an object due to gravity, measured in Newtons - because it is a force

weight ig an object isn’t constant - depends on the force of gravity experienced by the object

equation linking weight mass gravitational field strength

weight(N) = mass(kg) x gravitational field strength(N/kg)

weight and mass are…

directionally proportional

centre of mass

• where is our centre of mass

• where does weight act

• when are you less likely to fall

• for people our centre of mass is in our torso

• weight acts straight downwards from our centre of mass

• your less likely to fall if your centre of mass is closer to the ground

how can you change the shape of an object (3)

• compressing - two forces activing towards each other → ←

• stretching - two forces acting away from each other ← →

• bending - two forces balance to hold the object steady. Another force acts to bend the object

what’s the difference between elasticity vs inelastic

elasticity- returns to original shape once force removed

inelastic - remains deformed after force is removed

hooked law

equation linking force, spring constant and extension

force = spring constant X extension

finding the extension of a spring - RP

method

1. set up equipment by attaching 2 bosses and 2 clamps to a clamp stand, place a heavy weight on the clamp stand (to stop it from falling over), attach a metre ruler and spring to the clamps (the top of the spring must be at the zero point on the metre ruler or otherwise a zero error) and attaching a wooden splint to the bottom of the spring to act as a pointer (pointer must be horizontal or readings will be inaccurate) gs

2. read the position of the pointer on the meter ruler - this is the un strength length of the spring with no force attached

3. Then attach a one N wait on the spring and read the new position of the pointer on the meter ruler

4. Continue adding one Newton weight to the spring I’m reading the position of the pointer

5. write readings on your table and create a graph

finding the extension of a spring - RP

what does the graph look like (3)

directly proportional

linear (straight line)

spring is elastic because if you remove the weight the extention returns ro 0

finding the extension of a spring - RP

IDC variables

I - weight (N)

D - extention (m)

C - same spring

finding the extension of a spring - RP

equipment

• clamp stand

• boss

• clamp

• heavy weight - stops stand from falling over

• metre ruler - is vertical (as reading will be inaccurate otherwise)

• spring

• wooden splint (used as a pointer) - is vertical as otherwise it will be innacurate

• newton weights

what is the spring constant on hooks law

what is the relationship between extension and weight

the gradient → change in y. (extinction) / change in x (weight)

directionally proportional

limit of proportionality

amount of force that will inelastically deform a spring

newtons 2nd law equation

Force(N) = mass(Kg) X acceleration(m/s²)

Newtons 2nd law-RP

method

• the trolley is attached to a string on the runway

• as you add more and more mass to the weight hanger the trolley moves faster

• as the trolley passes the light gate it measures the acceleration and shows on the data logger so wr don’t have to measure

• repeat 3x and find a mean

Newtons 2nd law-RP

equipment

• trolley

• runway

• bench

• weight hanger

• string

• card - so it is rejusted as it goes through the light gate

• data logger

• light gate

Newtons 2nd law-RP

IDC variables

I - mass

D - acceleration

C - the same trolley, other equipment

what’s the relationship between force and acceleration

directionally proportional

define work

a force causes energy to be transferred into an object

• can be measured in Joules (is energy transfer) but can sometimes be measured in Newton Metres

Energy transfer

when a change in height happens there has been a change to the gravitational energy store

when a change in speed happens, there has been a change to the kinetic energy store

equation linking work done, force applied, distance moved

work done W (J or Nm) = force applied F (N) X distance moved s (m)

stopping distance define

the distance a car travels between seeing something that makes it need to stop and actually stopping

stopping distance (how far we travel before we stop)= thinking distance (how far you travel BEFORE hitting the brakes)+ braking distance(distance travelled AFTER vrakes have been pressed)

factors affecting breaking distance (6)

• road/weather condition

• weather condition - an incy wet road wold have a larger breaking distance than a dry road as it is more slippery

• tyre condition/age - older tyres =less grooves →less friction inc braking distance

• condition/age of cars brakes - car with older brakes/worse condition wont break as effectively

• speed - car going faster will have more momentum + will be harder to stop

• mass of vehical - heavy lorry will be harder to stop than a light weight smart car

Factors affecting thinking distance (5)

• distraction - loud music, conversation, PHONE

• drugs/alcohol - impairs judgement + lengthens reaction time/caffeen would improve

• speed of driving

• tiredness

• age

whats the force that is brought down by gravity

weight

terminal velocity

the top speed a falling object can reach

what jappens between when a skydiver falls drom a plane to being on the ground

sky diver leaves plain - sskdiver is speeding up quickly - more weight than air resistance

bit later - skydiver is still speeding up but less than before - air resistance increases as he gets faster

later still - sky diver is going at constant speed - ai resistance and weight are balanced

skydiver opens parachute - sky diver starts slowing down - air resistace is greater than weight

some time later - sky dver is going at a constant speed (terminal velocity) forces are balanced

skydiver has landed - sky diver is stood still/stationary - normal force and weight are balanced