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AQA Unit Two Physics
Cora Hurley…read more

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Velocity and Acceleration
Speed and Velocity are both how fast you are going
· Speed and velocity are both measured in m/s. They both simply say
how fast you are going however, speed is just how fast you are going,
with no regards to the direction. Velocity however must also have
the direction specified.
Speed, Distance and Time
· Speed=Distance/time
Acceleration is how quickly you are speeding up
· This is not the same as velocity or speed.
· Acceleration is how quickly the velocity is changing
· Acceleration =Change in velocity / Time taken…read more

Slide 3

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D-T and V-T Graphs
Distance-time graphs
· Speed = Gradient (vertical/horizontal)
· Flat sections are where it stopped.
· The steeper the graph, the faster its going
· Downhill sections means its going back towards the starting point
· Curves represent acceleration or deceleration
· A steepening curve means its speeding up
· A levelling off curve means its slowing down.
Velocity-time graphs
· Acceleration = gradient
· Flat sections represent steady speed
· The steeper the graph, the greater the acceleration or deceleration
· Uphill sections are acceleration
· Downhill sections are deceleration
· The area under any section of the graph is equal to the distance travelled
in that time interval.
· A curve means changing acceleration.…read more

Slide 4

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Mass, Weight and Gravity
Gravity is the force of attraction between all masses
· Gravity attracts all masses, but you only notice it when one of the masses is really big. E.g. a
planet; anything near a planet is attracted to it.
· This has 3 important effects:
· On the surface of a planet, it makes all things accelerate towards the ground.
· It gives everything a weight
· It keeps planets, moons, and satellites in their orbit. The orbit is a balance between the
forward motion if the object and the force of gravity pulling it inwards.
Weight and mass are not the same
· Mass is just the amount of stuff in an object. For any given object the mass will be the same
anywhere in the universe.
· Weight is caused by the pull of gravity. In most questions, the weight of an object is just the
force of gravity pulling it towards the centre of the earth.
· An object has the same mass whether it is on earth or on the moon-but its weight will be
· Weight is a force measured in newton's. Its measured using a spring balance or newton
metre. Mass is not a force. Its measured in kilograms with a mass balance.
The very important formula ­ Mass, weight and gravity.
· Weight = mass x gravitational field strength (W = m x g)…read more

Slide 5

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The 3 Laws of Motion
First law ­ balanced forces mean no change in velocity
· So long as the forces on an object are all balanced, then it will stay still, or else if it is already
moving it will just carry on at the same velocity ­ so long as the forces are all balanced.
· When a train or car or bus or anything else is moving at a constant velocity then the forces on it
must all be balanced.
· Never let yourself entertain the ridiculous idea that things need a constant overall force to
keep them moving.
· To keep going at a steady speed, there must be zero resultant force.
Second Law ­ A resultant force means Acceleration
· If there is an unbalanced force, then the object will accelerate in that direction
· An unbalanced force will always produce acceleration
· This acceleration can take five different forms: starting, stopping, speeding up, slowing down,
and changing direction
· On a force diagram the arrows will be unequal.
Three points which should be obvious
· The bigger the force, the greater the acceleration or deceleration
· The bigger the mass the smaller the acceleration
· The get a big mass to accelerate as fast as a small mass it needs a bigger force. Just to think
about pushing heavy trolleys and it should seem fairy obvious.
The overall unbalanced force is often called the resultant force
· Any resultant force will produce acceleration and the formula is:
· F= ma or a=F/m…read more

Slide 6

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The 3 Laws of Motion Cont.
Resultant force is really important ­ especially for F=ma
· The notion of resultant force is a really important one for you to get your head
· in most real situations there are at least two forces acting on an object along with
any direction. The overall effect of these forces will decide the motion of an object
­accelerate, decelerate or stay at a steady speed.
· If the forces all point along the same direction the overall effect is found by just
adding or subtracting them.
· The overall force you get is called the resultant force. F is always the resultant
The Third Law ­ Reaction Forces
· If object A exerts a force on object B then object B exerts the exact opposite force
on object A.
· This means if you push something, the object will push back against you just as
· As soon as you stop pushing, so does the object
· One object normally has a smaller mass, so will accelerate more.
· E.g. in swimming you push against the water with your arms and
legs, and the water pushes you forward with an equal- sized force in
the opposite direction.…read more

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