forces

• scalar quantities


  have magnitude (size) only
• vector quanities :


  have magnitude (size) and direction
• examples of vector quanities :


  • force
  • velocity
  • displacement
  • acceleration
  • momentum
• examples of scalar quantities :


  • speed
  • distance
  • mass
  • temperature
  • time
• what is a contact force 


  when 2 objects have to be touching for a force to act
• what is a non-contact force


  if the objects do not need to be touching for the force to act
• what is an interaction pair 


  a pair of forces that are equal and opposite and act on 2 interacting objects
• what is mass ?


  the amount of 'stuff' in an object, an object will have the same mass anywhere in the universe
• what is weight ?


  the force acting on an object due to gravity, it changes depending on the strength of the gravitational field
• how is mass measured and what units ?


  measured in Kilograms with a top pan blance
• how is weight measure and what unit?


  it is measured on a spring balance (or newton metre) and is measured in newtons
• mass and weight are directly proportional
• what is resultant force ?


  • the overall force on a point or object
  • if you have a number of forces acting at a single point you can replace them with a single force (the resultant force)
• when a force moves an object through a distance energy is transferred and work is done on the object
• when you apply a force to an object you may cause it to bend, stretch or compress

  for this to occur you need more than one force acting on the object (otherwise the object would simply move in the direction of the applied force instead of changing shape)
• elastic deformation:

  • an object has been elastically deformed if it can go back to its original shape and length after the force has been removed
  • objects that can be elastically deformed are called elastic objects
• inelastic deformation:

  • an object has been inelastically deformed if it doesnt return to its original shape and length after the force has been removed
• a moment is the turning effect of a force
• levers make it easier for us to do work :

  • levers increase the distance from the pivot at which the force is applied, since M=Fd this means less force is needed to do the same movement
• Gears :

  • used to transmit the rotational effect of a force from one place to another
  • different sized gears can be used to change the moment of the force , a force transmitted to a larger gear will cause a bigger moment as the distance to the pivot is greater
  • a larger gear will turn slower than the smaller gear
• the pressure of a fluid means a force is exerted normal (at right angles) to any surface in contact with the fluid
• density in fluids :

  • for a given liquid density is uniform and it doesnt vary with shape or size
  • the more dense a given liquid is the more particles it has in a certain space, this means there are more particles that are able to collide so the pressure is higher
  • as the depth of liquid increases, the number of particles above that point increases, the weight of these particles adds to the pressure felt at that point so liquid pressure increases with depth
• what is upthrust ?


  Upthrust is the upward force exerted on an object submerged in a fluid, such as water, due to the difference in pressure between the top and bottom of the object.
• if upthrust is equal to the objects weight then the forces balance and the object floats
• atmospheric pressure is created on a surface by air mollecules colliding with the surface

  • as altitude increases atmospheric pressure decreases
  • as altitude increases the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface
• distance is how far an object has moved and it is a scalar quantity
• displacement is a vector quantity, it measures the distance and direction in a straight line from an objects starting point to its finishing point
• velocity is a vector quantity, it tells us both speed and direction
• speed is a scalar quantity, it tells us how fast something moves but not which way it goes
• acceleration is a vector quantity, it tells us how quickly an object changes velocity
• Time- distance graph:

  • gradient = speed
  • flat sections are where its stationary
  • straight uphill sections = steady speed
  • curves represent acceleration or deceleration
• Velocity - time graph:

  • gradient= acceleration
  • flat sections = steady speed
  • the steeper the graph the greater the acceleration or deceleration
  • a curve means a changing acceleration
  • area under the graph= distance travelled in that time interval
• what is terminal velocity ?


  The maximum velocity an object can reach while falling through a fluid due to the balance of gravitational force and air resistance.
• what is newtons 1st law?

  if the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it'll just carry on moving at the same velocity
• acceleration is proportional to resultant force
• inertia is the tendency for motion to remain unchanged
• what is newtons third law?

  when 2 objects interact, the forces they exert on each other are equal and opposite
• what is thinking distance ?


  how far the car travels during the drivers reaction time (the time between the between the driver seeing a hazard and applying the brakes)
• what is the braking distance ?

  distance to stop under the braking force (once brakes are applied)
• stopping distance= thinking distance + braking distance