Forces

• Scalar quantities have magnitude only.
• Vector quantities have magnitude and an associated direction.
• Examples of scalar quantities include: temperature, mass, distance, speed, energy and density.
• Examples of vector quantities include: displacement, velocity, acceleration, force, momentum and weight.
• A force is a push or pull that acts on an object due to the interaction with another object. All forces are either contact or non-contact.
• Examples of contact forces include friction, air resistance, tension and normal contact force
• Examples of non-contact forces are gravitational force, electrostatic force and magnetic force.
• Does this diagram represent a scalar or vector quantity?

  A) vector

  
• Weight is the force acting on an object due to gravity.
• Why is the force of gravity close to the Earth?

  due to its gravitational field.
• The weight of an object depends on the gravitational field strength at the point where the object is.
• The weight of an object can be calculated using the equation:$W =$$m g$
• The weight of an object and the mass of an object are directly proportional.
• Weight is measured using a newtonmeter.
• what is the center of mass?

  the point where we can assume all the mass of the object is concentrated
• the resultant force is the single force that replaces all other forces acting on an object.
• A single force can be resolved into two components acting at right angles to each other. The two component forces together have the same effect as the single force.
• How do you draw a vector diagram?

  The forces are drawn to scale. They must be drawn tip to tail. The resultant force is then represented by drawing an arrow from the start of the first force to the end of the second force.
• When a force causes an object to move through a distance work is done on the object.
• The work done by a force on an object can be calculated using the equation: $W =$$F s$
• 1 joule = 1 newton-metre
• Work done against the frictional forces acting on an object causes a rise in the temperature of the object
• A change in shape is called deformation
• • elastic deformation is reversed when the force is removed
• inelastic deformation is not fully reversed when the force is removed
• why must more than one force be acting on an object to change its shape?

  because a single force would cause the object to move in the direction in which the force were to be applied
• force = spring constant × extension
• 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.
• what is hookes law?

  The extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
• If an object doesn't obey Hooke's law, there is a non-linear relationship between force and extension.
• calculate work done in stretching (or compressing) a spring (up to the limit of proportionality) using the equation:$Ee =$$1 /2 ke^2$
• force is directly proportional to extension
• label the diagram

  A) ruler

  B) spring

  C) mass hanger

  D) masses

  E) pointer

  F) clamp and stand

  
• Pressure can be calculated using: $p =$$F/ A$
• The turning effect of a force is called the moment of the force
• The size of the moment is defined by the equation:$M =$$F d$
• An example of a turning force is  when you push a door, the door will turn on its hinges.
• If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
• Levers and gears are capable of taking an input force and multiplying it at the output.