# AQA Physics Spec B Unit 2

general overview of all topics in AQA B unit 2 Physics.

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## 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

• 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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## Changing Forces

• 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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## Energy Changes

• 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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## Stopping Safely

• 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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