forces and motion

The speed of an object is the distance it travels per unit time.

what is the speed of an object?

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The velocity of a moving object is similar to its speed, except it also describes the object's direction.

what is the velocity of a moving object?

what is the formula for speed?

acceleration is how quickly the velocity is changing

what is acceleration?

what is the formula for acceleration?

what is the other formula for acceleration with distance involved?

tell you how far something has travelled

what do distance time graphs tell u?

gives you the speed of the object

distance time graph - gradient?

stationary

distance time graph - flat sections?

its going faster

distance time graph - steeper graph?

acceleration

distance time graph - curve?

acceleration

velocity time graph - gradient?

steady speed

velocity time graph - flat sections?

= to the distance travelled to find area u do area under graph

velocity time graph - area under graph?

changing acceleration

velocity time graph - curve?

gravity is the force of attraction between all masses

what is gravity?

1- on the surface of a planet it makes all things accelerate towards the ground- 10m/s or 9.8

2- it gives everything a weight

3- it keeps planets moons and satellites in their orbit

what are the 3 important effects of gravity?

the orbit is a balance between the forward motion of the object and the force of gravity pulling it inwards

what is an orbit?

mass is just the amount of matter in an object

what is mass?

caused by the pull of gravity.

what is weight caused by?

weight is the force of graver pulling it towards the centre of earth.

a force measured in newtons.

measured using a spring balance or newton meters.

what is weight?

mass is not a force

measured in kilograms with a mass balance

is mass a force and how is mass measured?

what is the formula relating mass weight and gravity?

1- gravity or weight- close to a planet this acts straight downwards

2- reaction force- acts perpendicular to a surface and away from it.

3- electrostatic force- between two charged objects. like charges repel, opposite charges attract

4- thrust- e.g push or pull due to an object speeding up

5- drag or air resistance or friction- slowing the object down

6- lift- due to an aeroplane wing

7- tension- in a rope or cable

what are the all the different types of forces?

friction is a force that opposes motion

what is friction?

%%1- friction between solid surfaces which are gripping%%

%%2- friction between solid surfaces which are sliding past each other:%%

reduce friction by putting a lubricant like oil or grease between the surface.

friction between solid can often cause wear of the 2 surfaces in contact.

%%3- resistance or drag from fluids:%%

keeping the object streamlined like sport cars.

lorries and caravans have deflectors on them to make them more streamlined and reduce drag.

roof boxes on cards spoil their streamlined shape and slow them down.

AS SPEED INCREASES FRICTION INCREASES

what are the three ways in which friction occurs?

the motion of a toy car on a ramp

practical: how can you investigate the motion of an object?

1- mark a line on the ramp- starting point

2- measure the distance between each light gate

3- let go of the car just before the light cate so it will start to roll down the slope

4- when the car passes through the light gate a beam of light will show and your time will come on the datalogger

5- repeat the experiment several time to get an average time of how long it takes for the car to reach each light gate

steps for practical of toy car?

if a stationary object’s resultant force is 0, the object will remain stationary. If a moving object’s resultant force is 0, the object will move in a constant velocity at same speed and direction

newton 1st law

zero resultant force

to keep a steady speed what must there be?

an object’s acceleration is directly proportional to the resultant force acting on it, and inversely proportional to the object’s mass

what is the second law of motion?

what is the formula relating force, mass and acceleration?

The forces that two objects exert on each other when they interact are equal and opposite

what is the 3rd law of motion?

vector quantise have a size and direction

force

velocity

acceleration

momentum

what is a vector quantity? and e.g

scalar quantities only have size and no direction.

mass

temperature

time

length

what is a Scalar quantity and e.g

hookes law says that extension is proportional to force

what does Hooke’s law say?

Natural length *I*

what is the length of an unstretched metal wire called?

it will stretch

if a metal wire is supported a the top and then a weight is attached to the bottom what will happen?

1- measure the length of the spring when no load is applied

ensure the ruler is vertical and measure the spring at eye level

2- add one mass at a time and allow the spring to come to rest then measure the new length of the spring.

the extension is the change in length from the original length

3- repeat the process until enough measurement

4- plot graph

investigation of Hooke’s law with a spring

the material will be permanently stretched

what happens if you increase the force past the elastic limit?

displays elastic behaviour.

if a material returns to its original shape once the forces are removed what does it display?

the stopping distance of a car is the distance covered in the time between the drive first spotting a hazard and the car coming to a complete stop.

what is the stopping distance of the car?

the distance the car travels in the time between the driver first noticing the hazard and applying the brakes

what is the thinking distance?

1- how fast ur going.- the faster ur going the further ul go

2- reaction time- affect by things like tiredness drugs alcohol and old age

what are the factors affect by thinking distance?

the distance the car travels during its deceleration whilst the brakes are being applied

what is the braking distance?

1- how fast ur going

2- the mass of the vehicle- the larges the mass the longer it takes to stop

3- how good your brakes are- all brakes must be checked

4- how good the grip is depends on three things :

road surface

weather conditions

tyres

what are the 4 factors affected by braking distance?

Momentum is defined as the product of an object's mass and velocity.

the greater the mass of an object and the greater its velocity the more momentum the object has

momentum is a vector quantity

what is momentum and formula?

momentum is conserved when no external forces act - total momentum after is the same as total momentum before

how is momentum conserved?

force

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what causes changes in momentum?

a faster change of momentum and so a greater acceleration

a larger force means?

longer it takes for a change in momentum, the smaller the force less sever

how are cars designed to slow people down over a longer time when they crash?

crumple on impact, increasing the time taken for the car to stop.

what do crumple zones do?

stretch slightly, increasing the time taken for person to stop.

reduces force acting on chest

what do seat belts do?

slows you down more gradually

what does air bag do?

a moment is the turning effect of a force about the pivot

what is a moment?/ formula

the force on the spanner causes a turning effect or moment on the nut.

a larger force would mean a larger nut

the force on the spanner causes what?

the same force can exert a larger moment because the distance from the pivot is greater.

what would happen to the force if you use a longer spanner?

you need to push at right angler perpendicular to the spanner

how can you get the maximum moment of the spanner?

if an object is balanced then total anticlockwise moments = total clockwise moments

what is the principle of moments?

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

object will turn

what happened in the moments are not equal?