Physics IGCSE Edexcel- Forces and Motion

Velocity

Speed in a given direction

Acceleration

The rate at which velocity changes

change in velocity can be...

To change speed, change direction or both.

unit for acceleration

m/s^2

Distance-time graphs

gradient= at any point gives the speed

flat line= object stopped/stationary

curve getting steeper= acceleration

curve levelling off= deceleration (slowing down)

Straight line= steady speed

line going back down= object going back to starting point

finding speed on a distance-time graph

speed = gradient = vertical/horizontal

finding average speed on a distance-time graph

average speed = total distance/total time

velocity-time graph

gradient= acceleration

flat line= steady speed

steeper line going up or down= greater acceleration or deceleration

uphill sections= acceleration

downhill line= deceleration

area under line= distance travelled in that time interval

curved line= changing acceleration

Acceleration on a velocity-time graph

acceleration = gradient = vertical/horizontal

gravity is...

the force of attraction between all masses

weight

Mass x gravitational field strength (10 on earth)

different types of forces

- gravity or weight

- reaction force

- electrostatic force

- thrust

- drag, air resistance or friction

- lift

- tension

Friction occurs in three main ways:

- static friction - between solid surfaces which are gripping

- sliding friction - between solid surfaces which are sliding past each other

- resistance or "drag" from fluids

The three laws of motion

1. balanced forces mean no change in velocity

2. a resultant force means acceleration

3. reaction forces

First law

Balanced forces mean no change in velocity, this means if an object is not moving then it will stay still, but if an object is already moving then it will carry on at the same velocity

Second law

A resultant force force means acceleration, if there is an unbalanced force (resultant force), then the object will accelerate in that direction.

equation for force

Force = mass x acceleration

Third law

reaction force, if object A exerts a force on object B then object B exerts an equal and opposite force on object A

vectors

quantities that have both a magnitude and a direction

scalars

quantities that have only a magnitude (do not include direction)

vector quantities

force, velocity, acceleration, momentum

scalar quantities

Mass, temperature, time, length

terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

terminal velocity of an object is dependent on...

the drag of an object. the drag depends on the shape and area

Hooke's Law

Extension is directly proportional to force until the spring reaches it's elastic limit

Hooke's law stops when...

the force becomes great enough. When you get to that point it is called the 'elastic limit', if you increase the force past the elastic limit the material will be permanently stretched

the two main factors affecting stopping distance

- thinking distance

- braking distance

Thinking distance is affected by...

-the speed you're going

-your reaction time (affected by age, drugs, tiredness etc)

Braking distance is affected by...

-how fast you're going (faster=further)

-the mass of the vehicle (bigger mass=longer to stop=go further)

-what condition you're brakes are in

-how good the grip is (depends on road surface, weather conditions, and tyres)

momentum equation

momentum=mass x velocity

momentum conservation

momentum before = momentum after

force and momentum equation

Force = change in momentum / time taken

larger force =

a faster change in momentum

moment equation

Moment = force x distance from pivot

a moment is...

the turning affect of a force

centre of gravity

The point where the entire weight of an object appears to act.

swinging with a centre of gravity

a freely suspended object will swing until its centre of gravity is vertically below the point of suspension

principle of moments - equal

total anticlockwise moments = total clockwise moments

principle of moments - unequal

If the total anticlockwise moments do not equal the total clockwise moments, there will be a resultant moment