Forces + motion

• Motion key words

  - acceleration

  - deceleration

  - change in direction

  - constant speed

  - stationary
• Contact forces


  - friction

  - thrust

  - tension

  - drag/ air resistance

  - reaction (normal force)
• Non contact forces


  - gravity

  - magnetism

  - electrostatic
• Newtons first law


  If there is no resultant force: an object stays stationary or keeps moving at constant speed in a straight line
• Newtons second law


  F = ma (if there is a resultant force, you will accelerate in it's direction)
• Newtons third law


  Every force has an equal and opposite reaction
• Hooke's law equation


  F = ke
• Hooke's law meaning


  A spring extension is directly proportional to the force, as long as the limit of proportionality is not exceeded
• A scalar has


  Magnitude
• A vector has


  Magnitude and direction
• Vector arrows rule


  Tip to tail

  
• Displacement


  How far an object has moved from it's starting position
• Solid pressure equation


  P = f/a
• Liquid pressure equation


  P = ρgh
• Gas pressure equation


  P₁V₁ = P₂V₂
• Factors affecting thinking distance


  - alcohol

  - tiredness

  - drugs

  - speed
• Factors affecting braking distance


  - speed

  - mass

  - tire + road quality

  - icy/ rain (bad weather conditions)
• Thinking distance + braking distance =


  Stopping distance
• Distance time graphs


  - gradient = speed

  - flat sections = stationary

  - straight = constant speed

  - curves = acceleration/ deceleration
• Velocity time graphs


  - distance travelled = area under graph

  - gradient = acceleration

  - flat sections = constant speed

  - curve = changing acceleration
• Velocity (v) =


  displacement (s) / time (t)
• Acceleration (a) =


  change in velocity (Δv) / time (t)
• Final speed² (v²) =


  Initial speed² + 2 x acceleration x speed (u² + 2as)
• Equibrilium

  No resultant force or moment
• A moment is...


  a turning effect
• Moment (M) =


  Force (f) x perpendicular distance (d)

  
• Work done (w) =


  Force (f) x distance (d)
• Weight (w) =


  Mass (m) x gravity (g)
• Distance (d) =


  Speed (s) x time (t)
• Force (f) =


  Mass (m) x acceleration (a)
• Momentum is


  - a vector

  - conserved when there is no external force
• Momentum (p) =


  Mass (m) x velocity (v)
• Momentum equation


  M₁V₁ = M₁V₂ + M₂V₃
• Change in momentum (∆p) =


  Force (f) x change in time (∆t)
• Seat belts/ crumple zones


  Force reduces = Time of contact increases = Effect of force decreases
• Elastically deformed objects...


  will return to their original shape and length
• Inelastically deformed objects...


  will not return to their original shape and length
• Limit of proportionality


  - the point at which the extension is no longer proportional to the force

  - is reached at a maximum force

  - will cause a curve on a graph
• Investigating springs experiment


  1. Measure the length of the string with no load with a millimetre rule clamped to the stand. Take a reading at eye level and mark the bottom of the spring

  2. Add a mass to the spring and allow it to settle. Record the mass and measure the new length of the spring. The extension is the change in length

  3. Repeat this process until there is enough measurements

  4. Plot a force-extension graph of your results

  
• Levers help doing work by...


  increasing the distance from the pivot so less force is needed for the same moment