AQA Physics Spec B Unit 2

Keeping Balanced

Objects in equilibrium will either be at rest or moving with a constant speed.
An unbalanced force means the object will accelerate.
For a static object, the horizontal and vertical forces must cancel out.
Add vectors 'Tip to Tail' when drawing a vector triangle to analyse objects in equilibrium.
For an object on a slope, e.g Skier, we can resolve weight into components parallel and perpendicular to the slope.
Parallel= Wcos theta
Perpendicular= Wsin theta

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Velocity and Acceleration are Vector quantities (meaning they have a magnitude and a direction)
v= change in displacement / change in time
A= change in velocity/ change in time
Distance-Time graph, Gradient = Acceleration
Speed-Time graph, Area below line= Distance, Gradient = Acceleration.
Equations of Motion apply to objects experiencing a constant acceleration e.g gravity.
Stopping Distance = thinking distance+ braking distance.

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Perpendicular vectors have no effect on each other- they are treated independantly.
A Projectile is an object subjected to the acceleration of free fall.
The horizontal motion is one of constant velocity ( thus acceleration is always zero)
Drag- resists movement of an object as it moves through a fluid. e.g air.
As an obect accelerates, so does the Drag force upon them.
When an obect is falling but drag is significant, F=M X A becomes F= M(g-A) where g= gravitational force.

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Work is done when a force causes an object to move.
W= Fs cos theta.
Gravitational Potential energy is when an object is raised.
Elastic potential energy is when an object is stretched/compressed.
Kinetic energy is energy of an object due to its motion.
Power is the rate of energy transfer with time.
when a sprinter runs, the energy transfer is Chemical energy to Kinetic Energy to Thermal and Sound Energy.

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Momentum is a vector quantity. p= mv (p=momentum, m=mass of object, v= velocity of object)
In an isolated system, total initial momentum= total final momentum.
When the system is subjected to a force or 'Impulse' (Fx change in t) momentum is not conserved.
Cars have crumple zones in order to increase the time over which a collision takes place, thus reducing the force on the driver, since mv=Fx change in t.
Seat belts and air bags use the same concept.
the longer an object is in contact with a force, the greater the momentum of the object when it is released. (e.g tennis racquet and ball)

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