forces

• scalar quantities only give magnitude
• vector quantities give magnitude and direction
• a force is a push or a pull that acts on an object due to its interaction with another object
• unit of force is a newton
• contact force occurs when two objects are physically touching
• Tension , friction and air resistance are contact forces
• normal contact force can only happen if two objects are in direct contact
• Magnetic and gravitational and electrostatic forces are non contact
• the mass of an object tells us how much matter is in it and it is measured in kilograms (Kg)
• mass does not change depending on location
• objects on earth experience a force of 9.8 N for every Kg of mass
• weight = mass x gravitational field strength
• the weight of an object is directly proportional to the mass of an object
• the gravitational field strength is a measure of the force of gravity in a specific location
• the weight of an object is the force due to gravity
• the weight can be considered to act at a single point called the centre of mass
• the resultant force is a single force that has the same effect as all the forces acting together
• to work out resultant force we take away the smaller force from the bigger force
• in a free body diagram the object is shown as point
• An object moving through the air experiences air resistance.
• Two objects sliding past each other experience friction forces.
• An object that is being stretched experiences a tension force.
• An object at rest on a surface experiences reaction force. 
• A magnetic force is experienced by any magnetic material in a magnetic field.
• An electrostatic force is experienced by any charged particle in an electric field.
• A gravitational force is experienced by any mass in a gravitational field.
• vector diagrams involve drawing a parallelogram and measuring the line from one tail of the shape to another
• whenever a force is used to move an object energy is transferred and this is called work
• work done = force x distance
• the unit of work is a joule
• the distance must be the line of action of the force
• elastic material always return to their original shape when forces stop acting on them
• elastic deformation is the change of an elastic objects shape
• in order to change an objects shape we must apply more than one force
• force = spring constant x extention
• speed in a direction is rarely constant
• velocity is the speed of an object in a given direction
• velocity and speed are calculated in the same way
• if an object is moving at a constant speed then its velocity is always changing for circular motion
• acceleration is the change in velocity over a given time