Higher Physics - Our Dynamic Universe

• equations of motion are for objects moving with ________ ___________ in a straight line

  constant acceleration
• first equation of motion


  v = u + at
• second equation of motion

  s = ut + 1/2at²
• third equation of motion

  v² = u² + 2as
• speed

  is the rate of change of distance, scalar quantity
• velocity


  is the rate of change of displacement, vector quantity
• acceleration


  is the rate of change of velocity, vector quantity
• displacement time graphs

  
• velocity time graphs

  
• velocity time graph for a bouncing ball

  -gradient of slope is constant

  -points get smaller in size than next point due to energy losses in the bounces

  
• newtons first law of motion

  if the forces on an object are balanced, the object will continue to travel with constant speed in a straight line
• newtons second law of motion

  if the forces acting on an object are unbalanced, the object will experience an acceleration
• unbalanced force equation

  
• in a lift you weight feels bigger than normal when:

  -accelerating upwards

  -decelerating downwards
• in a lift your weight feels smaller than normal when:

  -accelerating downwards

  -decelerating upwards
• in a lift your weight feels normal when:

  -travelling at a constant speed/zero/stationary
• velocity-time graphs and air resistance for a sky diver

  1) when the skydiver jumps out of the plane, she ACCELERATES due to the force of gravity

  2) As she speeds up as the upwards air resistance increases, thus reducing her acceleration

  3)eventually she reaches her TERMINAL SPEED when the air resistance balances her weight

  4)when parachute opens it has a large surface area which increases the air resistance, causing the unbalanced force upwards to increase and causes parachutist to slow down

  5)as parachutist slows down, her air resistance gets less until eventually it is balanced again by her weight, she falls at terminal speed, but slower terminal speed than before.
• three factors that cause an increase in the rockets acceleration:

  - gravitational field strength decreases with distance from the earths surface (weight decreases)

  - the rocket fuel is being used up as the rocket rises, the overall mass of rocket decreases ( weight decreases)

  - the atmosphere becomes thinner as the rocket rises (air resistance decreases)
• as the rocket gets further from the earths surface the gravitational field strength decreases resulting in a decrease in weight. this means that the _______________ _______ increases, this results in an increase in acceleration as a=f x m , f is increasing

  unbalanced force
• two vectors can be called the ________________ of the original vector

  components
• law of conservation of energy


  energy cannot be created or destroyed, it can only be changed from one form to another
• the momentum is the product of its _________ ____ _________

  mass and velocity
• units for momentum

  kgms-1
• formula for momentum

  
• law of conservation of momentum

  in the absence of external forces, the total momentum just before an event is the same as the total momentum just after the event
• in elastic collisions:

  -kinetic energy is conserved

  -momentum is conserved

  -the 2 colliding objects bounce apart after the collision
• in inelastic collisions:


  -kinetic energy decreases (kinetic energy is changed into sound, heat and energy of deformation which changes shape of the object)

  -momentum is conserved

  -the 2 colliding objects may bounce apart but can stick together
• explosions are when:

  there is only one stationary object at the start, this object splits into two parts which travel in opposite directions in a straight line
• in explosions:

  -momentum is conserved

  -kinetic energy decreases (the stored potential energy is changed into kinetic energy, when object explodes)
• newtons third law of motion


  if object a exerts a force onto object b, then object b exerts a force on the object a which is equal in magnitude but in the opposite direction
• the impulse is equal to:

  the average force multiplied by the time over which the force acts
• units for impulse

  Ns or Kgms-1
• impulse is equal to the ________ __ ____________

  change in momentum
• equation for impulse

  
• in force time graphs the area under the graph represents:

  -the impulse of the force exerted by the wall on the ball during its time of contact

  -the change in momentum experienced by the ball during its time of contact with the wall
• force time graph

  
• why does increasing the time of contact increase safety?


  as the impulse Ft is equal to the change in momentum during an impact, so we know that if t increases then the f must decrease to allow momentum to stay the same.
• the path traveled by the projectile is known as its ______________

  trajectory
• horizontal motion of projectiles

  - the Vh stays constant

  -no acceleration

  - d=Vh x t
• vertical motion of projectiles

  - the Vv increases with time

  - acceleration = -9.8ms-2

  - s=ut+1/2at²

  - if the projectile is fired horizontally, then u(initial speed)= 0ms-1