Forces

• Scalar quantities have magnitude only
• Vector quantities have magnitude and a direction.
• A vector quantity can be represented by an arrow. The length of the arrow represents the magnitude, and the direction of the arrow is the direction of the vector quantity.
• A force is a push or pull that acts on an object due to the interaction with another object
• forces are either:

  • contact
  • non contact
• contact forces are when the objects are physically touching
• non-contact forces are when the objects are physically separated.
• examples of contact forces:

  • air resistance
  • tension
  • friction
  • normal contact force
• examples of non contact forces:

  • gravitational
  • electrostatic
  • magnetic
• Force is a vector quantity.
• Weight is the force acting on an object due to gravity
• The force of gravity close to the Earth is due to the gravitational field around the Earth
• The weight of an object depends on the gravitational field strength at the point where the object is
• The weight of an object may be considered to act at a single point referred to as the object’s ‘centre of mass’.
• The weight of an object and the mass of an object are directly proportional.
• Weight is measured using a calibrated spring-balance (a newtonmeter).
• A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together. This single force is called the resultant force.
• When a force causes an object to move through a distance, work is done on the object
• So a force that does work on an object, causes a displacement of the object
• One joule of work is done when a force of one newton causes a displacement of one metre.
• 1 Joule = 1 Newton-metre
• you can change the shape of an object by:

  • bending
  • compressing
  • stretching
• elastic deformation is when the material returns to its original shape after the force is removed
• inelastic deformation is when the object is not able to return to its original shape after the force is removed
• The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
• A force that stretches (or compresses) a spring does work and elastic potential energy is stored in the spring.
• Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal.
• Distance is how far an object moves.
• Distance does not involve direction.
• Distance is a scalar quantity.
• Speed does not involve direction
• Speed is a scalar quantity
• The speed at which a person can walk, run or cycle depends on many factors including: age, terrain, fitness and distance travelled
• • walking ̴ 1.5 m/s
  • running ̴ 3 m/s
  • cycling ̴ 6 m/s
• A typical value for the speed of sound in air is 330 m/s.
• The velocity of an object is its speed in a given direction.
• Velocity is a vector quantity.
• If an object moves along a straight line, the distance travelled can be represented by a distance–time graph
• newtons first law states that a resultant force is needed for a change in motion
• newtons second law states that a non zero resultant force will cause an object to accelerate