AQA GCSE Physics - Forces

AQA GCSE Physics - Forces

1. Contact and Non-Contact Forces

   • Vectors - Have both magnitude and direction. Examples: force, velocity, acceleration
   • Scalars - Have only magnitude. Examples: speed, distance, mass
   • Contact force - A force acts only when two objects are touching. Examples: friction, air resistance, normal contact force
   • Non-Contact force - A force acts when the objects aren't touching. Examples: gravitational force, electrostatic force, magnetic force

2. Weight, Mass and Gravity

   • Gravitational force - the force of attraction between masses
     • This has two important effects: it makes all things fall towards the ground & it gives everything a weight
     • The gravity on Earth is approximately 9.8 N/kg
   • Weight - the force acting on an object due to gravity. Therefore the weight of an object changes in the universe since the gravity changes.
     • Weight is a force measured in Newtons (N), It can be measured using a calibrated spring balance or using a newton meter.
   • Mass - is the amount of "stuff" in an object. This object will have the same value anywhere in the universe
   • You are able to calculate the weight of an object with the equation: Weight (N) = Mass (kg) * Gravitational Field Strength (N/kg)
     • Weight is directly proportional to mass. Also written as: W ∝ m

3. Resultant Forces and Work Done

   • Free body diagrams - shows all the forces acting on an object. The size of the arrows show the relative magnitudes of the forces and the directions off the forces acting on the object.
   • Resultant force - the overall force on a point or object. In most real situations, there are at least two forces on an object in any direction. If you have more than one force acting at a single point, you can replace them with a single force. This single is the resultant force. If the forces all act along the same line (parallel), the overall effect is found by adding those going in the sane direction and subtracting any going in the opposite direction.
   • Work done - Work is done if a resultant force moves an object. The force does "work" to move the object and energy is transferred from one store to another.
     • When a force moves an object through a distance, ENERGY IS TRANSFERRED and WORK IS DONE on the object.
     • W-Work Done (J) = F-Force (N) * s-Distance (m)
     • 1 J = 1 Nm

4. Forces and Elasticity

   • When applying forces to an object, it may bend, stretch or compress. To do this you need more than one force acting on the object. If not, the object would only be caused to move in a direction.
   • Elastically deformed - when an object goes back to its original shape and length after the force has been removed.
   • Inelastically deformed - when an object is unable to return to its original shape and length after the force has been removed.
   • Extension - the extension of a spring is directly proportional to the force applied