Physics revision

• An object may have several forces acting on it-which can have different strengths and directions.But they can be added together to the resultant force. This is a single force that has the same effect on the object as all the individual forces acting together. 
• When all forces are balanced, the resultant force is Zero. In this case, a stationary object remains stationary and a moving object keeps on moving in the same direction at the same speed.
• When all the forces are not balanced, the resultant force isn't zero.In this case a stationary object begins to move in the direction of the resultant force and a moving object speeds up,slows down or changes direction depending on the resultant force. 

Law 1

• Every object will remain ar rest in a straight line unless compelled to change it's state by an external force.
• No force acting on an object=object will remain at a constant velocity.
• If velocity is zero, object will remain at rest, if external force applied, velocity will change.

Law 2

• F=m*a
  
• Defines force to be equal to change in momentum (m* velocity) per change in time
• For an object with a constant mas, the second law stated that the force is the product of an object's mass and it's acceleration.
• For an externally applied firce, the change in velocity depends on the mass of the object.
• A force causes a change in velocity, which likewise generates a force

Law 3

• Fa=-Fb
• States that for every action(force) in nature there is an equal and opposite reaction.
• If object a exerts a force on objectB, then object B exerts an equal force on object A
• Third law canbe used to explain lift by a wing and thrust by a jet engine.

Contact forces

• friction
• air resistance/drag
• tension/compression
• normal contact(reaction)
• Force/upthrust

Non-contact forces

• gravity
• electrostatic
• magnetic

weight(n)=mass(kg)*gravitational field strength(n/kg)

In any calculation the value of the gravitational field strength(g) is 10 unless otherwise stated

Weight is NOT the same as mass

On earth if you drop an object it accelerates towards the centre of the planet.

• The spring constant is a meaurement of how stiff a spring is.
• The stiffer the sping, the higher the sping constant.
• It is usually measured in Newtons per metre.
• Force=spring constant*extension
• F=K*e
• (N)=(N/M)*(M)