Forces

• Force is a vector quantity
• Vector quantities have a magnitude and direction
• Magnitude refers to the size or amount of something, while direction refers to where it's pointing.
• Forces are measured in newtons (N)
• Examples of vector quantities: Force, velocity, displacement, acceleration and momentum
• Scalar quantities only have magnitude and no direction
• Examples of scalar quantities: speed, distance, mass, temperature, time
• Vectors are usually represented by an arrow - the length of the arrow shows the magnitude and the direction of the arrow shows the direction of the quantity
• Velocity is a vector quantity, but speed is a scalar quantity
• Forces can be contact or non-contact
• A force is a push or pull on an object that is caused by it interacting with something
• When 2 objects have to be touching for a force to act, that force is called a contact force
• Examples of contact forces: friction, tension in ropes, air resistance
• If the objects do not need to be touching for the force to act, the force is a non-contact force
• Examples of non-contact forces: magnetic force, gravitational force, electrostatic force
• When 2 objects interact, there is a force produces on both objects
• An interaction pair is a pair of forces that are equal and opposite and act on 2 interacting objects
• Gravitational force is the force of attraction between masses
• Gravity attracts all masses and has important effects

  • On the surface of a planet, it makes all things fall towards the ground
  • It gives everything a weight
• Weight and mass are not the same
• Mass is how much matter an object contains (kg)
• An object will have the same volume of mass anywhere in the universe
• Weight is the force acting on an object due to gravity (the pull of the gravitational force on the object.
• Gravitational field strength varies with location
• The weight of an object depends on the strength of the gravitational field at the location of the object. The weight of an object changes with its location
• Weight is a force measured in Newtons
• Weight is measured using a calibrated spring balance or a newtonmeter
• Mass is not a force
• Mass and weight are directly proportional
• Weight = mass x gravitational field strength
• For Earth, the gravitational field strength is 9.8 N/kg
• Increasing the mass of an object increases its weight
• Free body diagrams show all the forces acting on an object
• In a free body diagram, the sizes of the arrows show the relative magnitudes of the forces and the directions how the direction of the forces on the object
• A resultant force is the overall force on a point or object
• If a resultant force moves an object, work is done
• When a force moves an object through a distance, energy is transferred and work is done on the object
• Work done = Force x distance (moved along the line of action of the force)
• W = Fs
• 1 joule of work is done when a force of 1 Newton causes an object to move a distance of 1 metre