Forces

• Vector quantities have both magnitude and direction.
• Examples of vector quantities are displacement, velocity, acceleration and force.
• A scalar quantity has only one value (magnitude).
• Examples of scalar quantities include distance, speed, mass, time and temperature.
• A force is a push or pull acting on something.
• Forces can be either contact or non-contact.
• Examples of contact forces are friction, air resistance, tension and normal contact force.
• Examples of non-contact forces are gravitational, electrostatic and magnetic force.
• Mass is the same anywhere in the universe.
• Weight is affected by gravitational field strength.
• Mass is measured in kg.
• Weight is measured in newtons.
• Weight (N) = mass (kg) x gravitational field strength (N/kg)
• Weight and mass are directly proportional.
• Free body diagrams are used to show all the forces acting on an object. The sizes of the arrows show the relative magnitude and direction of the force.
• Resultant force is the sum of the forces acting on an object. You can find it by adding forces that are working in parallel.
• When a force moves an object through a distance, energy is transferred and work is done.
• Work done (J) = Force (N) x Distance (m)
• 1 joule = 1 newton metre
• Scale drawings can be used to find resultant forces. The resultant force here is drawn in red.

  
• An object is in equilibrium if all its forces are balanced (they sum to zero). On a scale diagram, this means the tip of the last force should meet the tail of the first force (e.g. form a triangle if there are three forces).
• You can split forces into components if they are at awkward angles (the lines in black can be components of the red line). Together they have the same effect as the red line.

  
• You need to apply more than one force to an object to get it to stretch, compress or bend.
• An object has been elastically deformed if it can go back to its original shape after the force has been removed (and inelastically if it doesn't).
• The extension of a spring is directly proportional to the force applied (Hooke's law)
• A stiffer spring has a greater spring constant.
• There's a limit to how much force you can apply to a spring - this is the limit of proportionality. On a graph, this is where the line starts to curve.
• The equation for elastic potential energy is: E = 1/2 x spring constant x extension squared
• The moment is the turning effect of a force.
• The size of a moment is given by: M=Fd
• A longer distance from the pivot means a larger moment.
• To get the maximum moment of a force, the force must be applied at 90 degrees (perpendicular) to the lever.
• If the total anticlockwise moment equals the total clockwise moment about a pivot, the object is balanced and won't turn.
• Levers increase the distance from the pivot at which the forces are applied and make it easier to do work.
• Gears are used to transmit rotational effects from a force from one place to another.
• A force transmitted to a large gear will cause a bigger moment as the distance to the pivot is greater.
• Fluids are substances that can flow e.g liquids and gases.
• As the particles in a fluid move around, they collide with the surfaces of other objects and particles. This exerts pressure.
• Pressure is exerted at right angles (normal) to the surface.
• Pressure = force/area