Physics Paper 1: Forces

• What is a scalar quantity and what are some examples?

  Scalar quantity - only has magnitude e.g speed, mass, distance, energy, temp and time
• what is a vector quantity and what are some examples

  vector quantity - has magnitude and direction e.g velocity, force, momentum, weight, acceleration and displacement
• what is velocity

  speed in a given direction e.g 30mph north
• what is the formula for objects travelling at constant speed?


  distance (m) = speed (m/s) x time (s)
• what are some typical speeds of transport?

  v
• what is acceleration and what is the general equation?

  rate of change of velocity - equation = a = (v-u)/t
• what is uniform acceleration and what is the equation?

  v(squared) - u =2×a×s - , in free fall is 10m/s2
• how to find speed in straight lines and curved lines?


  straight lines - change in y / change in x
• how to find speed in curved lines?

  draw a tangent at the curved and find speed of the tangent - straight lines
• in velocity time graphs - how to find the distance travelled in the area under the graph?

  split into triangles and rectangles and count squares and do squares on yaxis divided by x axis
• what is newtons 1st law?

  where the resultant force on a body is zero, i.e. the body is moving at a constant velocity or is at restwhere the resultant force is not zero, i.e. the speed and/or direction of the body change(s)
• what is newtons 2nd law?

  larger resultant force - accelerates more as rf and a are directly proportional, and acceleration is inversley proportional to mass so force = mass x acceleration
• How to prevent large decaccelration? - large force causes injuries

  force can be lowered - slowing object down: seatbelts, airbags - increases collision times and reduces force (slow down gradually)
• Describe how weight is measured and what it is

  weight - force acting on an object due to gravity, (centre of mass) - measured in newtons by a newton meter
• what is mass and what is it measured by?

  amount of matter in some given value, measured in kilograms by mass balance
• Describe the relationship between the weight of a body and the gravitational field strength

  weight (N) = mass (kg) x GFS (N/KG) - The weight of an object is directly proportional to its mass and the gravitational field strength of the planet it's on. Which is shown in the formula So, for a given mass, the weight increases with higher gravitational field strength, and for a given gravitational field strength, the weight increases with higher mass.
• What is circular motion?

  If velocity is travelling in a circle so it is changing direction a lot - changing velocity - to accelerate, gravity must be acting on the object
• what is centripetal force?

  force acts on weaker centre of a circle
• Core Practical: Investigate the relationship between force, mass and acceleration by varying the masses added to trolley

  1. measure mass of trolley, masses and hook
  2. measure the length of the card -and between the light gates (distance)
  3. adjust height of ramp when trolley is just moving
  4. mark line on ramp before light gate and when travel some distance, record inital speed
  5. attach trolley to hanging mass - let it go and roll down
  6. the light gate will record time + speed when the trolley passes through
  7. find acceleration = change in speed (1st and last light gate)/ time (time takes to travel between)
• results of trolley practical?

  you should find that force and acceleration are proportional and mass and acceleration are inversley proportional
• Explain inertial mass + inertia

  inertia - tendency for motion to remain unchanged (moving with same velocity

  inertial mass - how difficult it is to change velocity of an object so to find 1 mass - rearrange the f = m x a equation = mass = f/a (ratio of force/acceleration
• What is newtons 3rd Law?

  (action reaction) - when 2 objects interact, the forces they exert on each other are equal and opposite pushes trolley - pushes back at you
• Define momentum, recall and use the equation:

  product of mass and velocity (how much oomph) - equation = p = m(kg) x v (m/s) - greater mass/velocity = more momentum
• what is the conservation of momentum?

  (in a closed system) - total momentum before collision = total momentum after collision
• Describe examples of momentum in collisions?

  momentum of snooker balls - (same size and mass) =

  • before collision - red ball has zero momentum (stationary) + white is moving with velocity and has momentum of p = m x v
  • after collision - when white ball hits red, red moves - has momentum, while white ball moves but has smaller velocity/momentum
  • conservation of momentum (in this scenario) = combine momentum of red and white balls = to original momentum of white ball before collision
• what is change in momentum?

  -when resultant force = acts on an object for sometime and ACCELERATES it - so force in any time changes velocity
• what is the equation for change in momentum?

  force (N)= mv- mu/t (s) = change in momentum/time

  • faster in change in momentum = bigger force
  • when momentum changes quicker - larger force need = injury
  • larger acceleration = larger the force
• what is the reaction time experiment?

  1.Arm resting on table, another person holds ruler between thumb and forefinger and the 3rd person should be eye - level with ruler

  2. without warning, person drops ruler and other person catches ruler with thumb and measure how long you caught it - long distance = longer reaction time

  3. calculate how long ruler was falling using acceleration equation (uniform one)

  4. repeat to make fair and accurate test + keep variables the same + get the average distance
• what is the stopping distance of a vehicle made up of? and what is it

  SD - driver spotting hazard and vehicle stopping = Thinking distance + Braking distance
• what is the thinking distance and what factors affect it?

  TD - distance car travels in drivers reaction time (noticed hazard and applied breaks, - factors = speed, drugs, reaction time - alcohol and tiredness
• what is breaking distance and what factors affect it?

  BD- distance taken to stop once breaks are applied - factors = speed (faster = longer stop), mass of car (wont stop quickly if heavy), brakes conditions (faulty - wont break with full force), friction between tyres + road (dirty, icy, wet = skid/slip)
• Estimate how the distance required for a road vehicle to stop in an emergency varies over a range of typical speeds

  to avoid accident - drivers must leave enough space at the front of the car to stop safely

  use speed limits as speed affects stopping distances, (as speed increases = thinking increases) as drivers reaction time is constant also braking distance + speed = squared relationship - when speed x 2, braking distance x 4
• Carry out calculations on work done to show the dependence of braking distance for a vehicle on initial velocity squared

  energy in cars KE store = work done by brakes

  1/2 x m x v (squared) = f (braking force) x d (braking distance )

  in explanation form: to stop car, brakes must transfer all energy from cars KE store to brakes TE store