Equations of Motion
v = final velocity
u = initial velocity
a = acceleration
t = time
s = displacement
1) v = u + at
2) v^2 = u^2 + 2as
3) s = ut + 0.5at^2
4) s = (u + v)/2 x t
Newtons Laws of Motion
1) An object will continue at a state of rest (or constant velocity) unless a resultant force acts upon the object.
2) Force is directly proportional to the acceleration providing mass is a constant,
i.e. F = ma
3) Each action has an opposite but equal reaction.
For Law 3...
SIMILARITIES - same type of force, same magnitude
DIFFERENCES - acting on different objects, in opposite directions
Resolving Vectors and Pythagoras
For those not so maths minded, a really simple way to do these questions is to learn the rule:
Vertical componants - use SIN
Horizontal componants - use COS
When finding the ANGLE, dont forget to use the INVERSE... One way to remember this is that both Angle and Inverse start with a vowel ;)
The same rules are applied with projectile motion. There is a great diagram on page 37 of the text book which shows this well (under the dartboard).
Conservation of Energy, Efficiency and Horsepower
The law of conservation of energy is simple:
ENERGY CANNOT BE CREATED OR DESTROYED
However, energy is transferred and for that reason we can work out its efficiency by this equation:
EFFICIENCY = (useful energy output/ total energy input) x 100%
Horsepower is a method of measuring the rate of doing work which was used before the industrial revolution.
1 Horsepower = 750 Watts
(don't forget that number!)
Equations You Should Really Know...
Power = energy transferred / time
Gravitational Potential Energy = mass x gravity x height
Kinetic Energy = 0.5 x mass x velocity^2
Work Done = Force x Displacement (in the direction of the force!)
Density = Mass / Volume
Force = Constant (k) x change in extension
Stokes Law (viscous drag) = 6(pi) x viscosity of the liquid (Pascal seconds - Pa s) x radius (metres) x drift velocity (ms^-1)
These may be in the formula booklet but they dont give the meanings of each term, so get familiar! :)
Definitions to learn:
Laminar Flow - streamline flow with no mixing, air flows in layers.
Turbulent Flow - flow with mixing of layers, forms eddies
Upthrust - weight of fluid displaced
Limit of Proportionality - when stress is proportional to strain and obeys Hooke's Law
Tensile strength - greatest stress before fracturing
Yield Point - point at which plastic deformation begins