Physics Paper 2 - Forces

• Scalar quantities have magnitude (size) only, no direction.
• Examples of scalar quantities include: mass, temperature, speed, time, distance and energy.
• Vector quantities have both magnitude (size) and direction.
• Examples of vector quantities include: displacement, weight, force, velocity, acceleration and momentum.
• Vectors can be represented by arrows. The length of the arrow represents the magnitude of the vector. The direction of the arrow represents the direction of the vector.
• A force is a push or a pull that acts on an object due to the interaction with another object.
• All forces have both magnitude (size) and a direction.
• The unit of force is the Newton (N).
• Contact forces are forces that act between two objects that are physically touching each other.
• A normal contact force is the upwards and downwards forces that are exerted between two objects that are in contact with each other.
• Non-contact forces are forces in which the two objects are physically separated.
• The mass of an object is the amount of matter in the object.
• The unit of mass is kilogram (kg).
• The weight of an object is the force acting on it due to gravity.
• The unit of weight is the Newton (N).
• The weight of an object depends on where it is, however the mass of it does not.
• The gravitational field strength is a measure of the force of gravity in a particular location.
• Objects on the surface of the Earth experience a force of 9.8N for every kg of their mass.
• weight (N) = mass (kg) x gravitational field strength (N/kg)
• The weight of an object is directly proportional to the mass of the object.
• Newtonmeters can determine an object's weight.
• The weight of an object (the force due to gravity) can be considered to act at a single point. This point is called the centre of mass.
• The resultant force is a single force that has the same effect as all of the original forces acting together.
• To work out the resultant force, you subtract the smaller force from the larger force.
• Whenever a force is used to move an object, energy is transferred. This is called work.
• work done (J) = force (N) x distance (m)
• Elastic materials will always return to their original length or shape if the forces acting on them are removed. This is called elastic deformation.
• force (N) = spring constant (N/m) x extension (m)
• When an elastic object is stretched or compressed, a force is being used to do work. Elastic potential energy is stored in the object. The work done is equal to the elastic potential energy.
• The turning effect of the force is called the moment of the force.
• moment (Nm) = force (N) x distance (m)
• When calculating moments, the distance must be perpendicular from the line of action of the force to the pivot.
• speed (m/s) = distance (m) / time (s)
• normal walking speed: 1.5 m/s
• running speed: 3 m/s
• cycling speed: 6 m/s
• car on main road: 13 m/s
• fast train in UK: 50 m/s
• cruising aeroplane: 250 m/s
• speed of sound in air: 330 m/s