- 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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- 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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