Forces

Forces

1. Forces and work done

   • Scalar
     • Speed
     • Distance
     • Overall
   • Vector
     • Velocity
     • Displacement
     • In a certain direction
   • Contact forces touch the object
   • Non-contact can act without touching the object, e.g. gravity
   • Resultant force diagrams
     • If forces cancel out, the object doesn't move
   • W.D = force * distance

2. Stretching and turning

   • Deformations
     • An elastic deformation is one which returns to its origional shape
     • An inelastic one is one that doesn't return to its original shape
   • The spring constant is k when force = k*extention
     • found in force-extension graphs by the gradient
     • Are under the graph = elastic energy stored
   • Moments
     • Moment of a force = force * distance
     • Bigger distance = bigger force
     • for an object to balance, the clockwise and anticlockwise moments must be the same
   • Gears rotation changes for each gear connected

3. Pressure

   • pressure = force / area
   • measured in pascals
   • Pressure increases the deeper you are in a liquid as there is more liquid on top of you
     • Pressure(pa) = depth(m) * density(kg/m^3) * gravitational field strength(N/kg)
   • Upthrust occurs when the pressure at the bottom of an object is greater than the pressure at the top
   • Atmospheric pressure decreases with height

4. Motion

   • displacement is the distance from one point to another in one direction
   • distance is how far something has traveled
   • Acceleration = velocity/time
   • Uniform acceleration means accelerating at a constant rate
   • The gradient of a distance-time graph = speed
   • The gradient of a velocity-time graph = acceleration
   • Terminal velocity is the speed at which the deceleration from air resistance = acceleration from gravity so an object stops accelerating
   • Newtons laws
     • An object needs a force to move
     • Acceleration is directly proportional to resultant force
     • each action has an equal and opposite reation
   • Inertia is the tendency for an object's motion to remain unchanged

5. Car safety and momentum

   • Stopping distance = thinking distance + braking distance
   • reaction times
     • factors
       • speed (both the distance over time and the drug)
       • Reaction time
         • tiredness
         • drugs
         • alcohol
     • average reaction times
     • Tests
       • Drop a ruler unexpectedly and see where they catch it
       • Identify when colour changes and how long it was since the colour actually changed
   • Breaking time factors
     • Speed (not the drug this time)
     • weather
     • Tyre condition
     • How good the brakes are
   • Momentum is vector
   • Cars are designed to stop a person over a longer period of time to make the force lower