Forces

• Conservation of momentum

  Momentum before = Momentum after
• Factors affecting stopping distance

  • Being on drugs
  • Drunk driving
  • Fatigue
• Momentum


  Momentum = p = mass x velocity
• Acceleration

  Acceleration = change in velocity / time taken
• Newton's laws

  1st Law: When the resultant force acting on an object is 0, the object is either stationary or moving at a constant speed. 2nd Law: When an unbalanced force acts on an object it accelerates. 3rd Law: Every force has an equal and opposite force.
• Thinking distance is the distance a car travels while the driver reacts
• Speed and velocity differ when an object is travelling in a circle at a constant speed
• Stopping distance is the sum of thinking distance and braking distance
• Change in momentum

  (Initial momentum - final momentum) / time
• Fluid

  Pressure in a fluid = Force normal to a surface / Area of that surface
• Distance-time graphs can represent an object's distance as it travels on a straight line
• Braking distance is the distance a car travels while the car is stopped by the brakes
• Atmospheric pressure decreases as you travel higher above the Earth's surface
• Velocity-time graphs: Gradient = acceleration, Area under graph = distance travelled
• Floating occurs because weight is the same as upthrust
• More than one force is needed to change the shape of an object
• 1 Joule = 1 Newton-meter
• Moment


  The turning effect of a force about a pivot
• Inelastic deformation occurs when an object does not return to its original length after all the forces are removed
• What happens to pressure as the density of air decreases?

  Pressure decreases
• Non-Contact force

  Exerted between two objects that are physically separated
• Elastic Deformation occurs when an object returns to its original shape after the forces are removed
• Vector

  A quantity with a magnitude and a direction
• Pressure in a column

  P = height of column x density of liquid x gravitational field strength
• Work done + energy transfer

  Work done = W = Fs (J), where W is work done, F is force, and s is distance moved
• Scalar quantities

  • Mass
  • Speed
  • Distance
• Contact Force

  Exerted when two objects touch
• Scalar


  A quantity with just a magnitude
• Contact forces

  • Friction
  • Air resistance
  • Tension
• Resultant force is a single force that can replace all the forces acting on an object
• Pressure in a gas

  P = F/A (at right angles), where P is pressure, F is force normal to a surface, and A is the area of that surface
• Moment


  Moment = Force x distance (Nm), where longer distance increases the force on the other side
• Vector quantities

  • Weight
  • Velocity
  • Displacement
• Stretching a spring

  Force needed = F = kx, where k is the spring constant and x is the extension
• Weight is the name given to the pull of gravity on an object
• Non-contact forces

  • Gravity
  • Electrostatic forces
  • Magnetic forces