forces

• momentum


  a vector quantity

  a product of an objects mass and velocity

  increased mass or velocity increases momentum

  in closed systems, momentum is conserved
• newtons first law

  an object will remain stationary or moving at a constant velocity of there is no resultant force acting on it
• newtons second law

  an objects acceleration is directly proportional to the resultant force acting on it and inversely proportionally to its mass
• newtons third law

  when two forces interact, the forces they exert on each other are equal and opposite
• thinking distance

  distance taken to stop travelling under breaking force

  affected by speed and reaction time
• vectors are magnitude and direction

  eg displacement, force, velocity
• contact force - force that is exerted between two objects that are in contact with each other eg friction, air resistance
• mass


  the amount of stuff in an object, so it does not change

  measured in kg
• weight


  the force on an object due to gravity

  changes based on gravitational field strength

  measured in N
• center of mass


  the point which weight is considered to act
• when a force moves an object through a distance, work is done as energy is transferred
• elastically deformed objects revert back to its original shape and length after the force is removed
• elasticity

  to stretch, compress or bend an object, there must be more than 1 force acting on it

  force is directionally proportional to extension

  when an object reaches its limit of proportionally, force is no longer proportional to extensional
• moments

  tuning effect of a force

  the larger the force or longer the distance, the greater the moment

  the force works perpendicularly to the distance

  a large gear causes a bigger moment

  measured in Nm
• fluid pressure

  in a liquid, density is uniform

  when something is more dense, there are more particles in an area so more collisions therefore an increased pressure

  measured in Pa (pascals)
• upthrust

  objects in fluids experience upthrust

  upthrust is equal to the weight of the displacement an object causes

  when an objects weight is equal to upthrust, it will float

  objects denser then the fluid will sink
• distance is scalar
• displacement is a vector ( both distance and direction)

  eg a walk 200m north then 200m south has 0 displacement
• an object moving in a circle at a constant speed has a constantly changing velocity
• walking - 1.5 m/s

  running - 3 m/s

  cycling - 6 m/s

  car - 25 m/s

  train - 30 m/s

  plane - 250 m/s
• acceleration is how quickly you speed up

  acceleration due to gravity is uniform for all objects in freefall

  it is the gradient in velocity - time graphs

  measured in m/s^2
• terminal velocity

  falling objects in fluids reach a terminal velocity, when friction is equal to acceleration so there in no resultant force on the object

  dependent on shape and area
• inertia 


  how difficult it is to change an objects velocity
• stopping distance = breaking distance + thinking distance
• breaking distance

  distance taken to stop moving once the breaks are applied

  affected by: speed, weather, road surface, tire conditions