forces

• What is friction?

  the contact between 2 moving objects or materials. Always opposes motion
• What is air resistance?

  friction due to the movement of an object through air. Also known as drag
• What is thrust?

  a force that pushes an object forwards
• What is tension?

  a force than pulls or stretches an object
• What is compression?

  a force that pushes or squeezes an object
• What is normal contact force?

  a force that reacts to an object preventing it from falling
• What is lift?

  a force that pushes or pulls an object up e.g. aeroplane
• What is upthrust?

  a force acting up on an object in fluid (liquid or gas)
• What is magnetic?

  a force between 2 magnetic materials (attractive or repulsive)
• What is electrostatic?

  a force between 2 charged objects (attractive or repulsive)
• What is gravitational?

  a force between 2 masses (always attractive)
• what do forces do?

  start or stop moving

  accelerate or decelerate

  change direction

  spin or turn
• what is mass?

  a measure of the amount of matter in an object.

  an object's mass will be the same whether it is on Earth, on the Moon or deep in space with no gravity
• what is weight?

  the force acting on the mass due to gravity.

  An objects weight depends on the gravitational field strength acting on it. So an object will weigh less on the Moon than on Earth because gravity is weaker on the Moon
• What is the resultant force?

  when more than one force acts on an object, we can combine them all into one force that would have the same effect as all the others added together.

  for any 2 forces opposite each other, subtract one from the other to find the resultant force.

  if 2 forces are in the same direction, add them together
• what is Newton's first law?

  If the object is stationary the object will continue to be stationary

  If the object is moving, the object will continue moving with its existing velocity
• What is Newton's second law?

  A resultant force acting on an object will cause it to accelerate in the direction of the force.

  The bigger the force the greater the acceleration

  The smaller the mass the greater the acceleration
• What is Newton's third law?

  when an object exerts a force on another object, the second object exerts an equal but opposite force on the first
• what is inertia?

  a reluctance to change velocity (speed or direction)
• what is inertial mass?

  a measure of an objects reluctance to change its velocity.

  It is the same value as normal mass, just a different definiton
• What factors affect thinking distance?

  reaction time

  alcohol / drugs

  distractions (e.g. phone, children)

  tiredness

  speed
• what factors affect braking distance?

  road conditions (e.g. ice, snow)

  mass of car

  speed

  tyre conditions

  brake conditions
• what are the energy transfers when braking?

  the energy in the kinetic store of the car is mechanically transferred to the thermal energy store of the brakes due to the friction in the brake pads
• explain why a stationary object can only change its shape (stretching, compressing or bending) if more than once force is acting on it

  a single force would just try to move the object

  to change shape, forces must act in different directions so the object stays still but becomes deformed
• what does 'in equilibrium' mean?

  all the forces acting on an object balance out so the object does not accelerate and it can either stay still or move at a constant velocity
• what does a free body diagram show?

  all the forces acting on a single object
• explain what it means if an object is falling freely under gravity

  the object is only moving because gravity is acting on it, there is no air resistance or any other force acting on it
• describe the motion of an object that falls through a fluid, eventually reaching terminal velocity

  starts off with initial acceleration because gravity is acting on it

  increasing fluid resistance, as the object speeds up, it pushes against the fluid creating a drag force.

  then the forces balance out

  then the object reaches terminal velocity
• what is terminal velocity?

  the fastest speed an object can reach while falling, without speeding up anymore
• what is the typical range of human reaction times?

  150 - 300 milliseconds
• what are the dangers involved in large decelerations of vehicles?

  injury to passengers

  damage to vehicle and other road vehicles

  vehicle control loss