General Stuff

• A force is any push or pull
• Types of forces


  • Contact forces
  • Non-contact forces
• Contact forces


  When objects are physically touching like when you push a door
• Non-contact forces


  Forces like magnetism, electrostatic forces and gravity
• Even contact forces are due to the electrostatic repulsion between electrons in your skin and the door
• Examples of contact forces

  • Normal force
  • Friction
  • Air resistance
  • Tension
• Force vector


  An arrow that shows the direction and magnitude of the force
• Magnitude of a force

  The size of the force, indicated by the length of the arrow
• Finding the resultant force

  1. Technically adding the vectors

  2. If forces are in opposite directions, one must be negative
• Finding the resultant force for vectors at right angles

  1. Use Pythagoras

  2. Use trigonometry (SOHCAHTOA)
• Balanced forces


  Forces that add up to zero, meaning the object will not accelerate
• Balanced forces do not necessarily mean the object is not moving, it could be moving at a constant velocity
• Newton's first law


  An object's motion is constant if there is no resultant force
• Scalar


  A quantity that has magnitude but no direction
• Examples of scalars


  • Distance
  • Speed
• Vector


  A quantity that has both magnitude and direction
• Examples of vectors


  • Displacement
  • Velocity
  • Weight
• Weight


  The force due to gravity acting on an object, calculated as mass * gravitational field strength
• 1 kg of mass on Earth has a weight of 10 Newtons
• When lifting an object at constant speed

  The upward force must equal the weight of the object
• Calculating work done


  Work done = Force * Distance moved
• Gravitational potential energy


  The energy gained when an object is lifted, calculated as mass * gravitational field strength * height
• Hooke's law


  Force = Spring constant * Extension
• Spring constant


  The stiffness of a spring, measured in Newtons per meter
• The energy stored in a spring is equal to 1/2 * k * (extension)^2
• Moment


  A turning force, equal to force * perpendicular distance to the pivot
• If the clockwise and anticlockwise moments are balanced, the object will not turn
• Principle of moments


  If the clockwise and anticlockwise moments are balanced, the object will not turn
• Gears are an application of moments
• Speed


  Distance divided by time
• Velocity


  Speed with direction
• Calculating speed or velocity from a distance-time graph


  The gradient of the graph gives the speed or velocity
• Calculating acceleration from a velocity-time graph

  The gradient of the graph gives the acceleration
• Acceleration


  The rate of change of velocity, measured in m/s^2
• For an object falling, the acceleration is 9.8 m/s^2 (the same as gravitational field strength)
• Calculating distance from a velocity-time graph

  The area under the graph gives the distance travelled
• Newton's equations of motion

  Equations relating displacement, initial velocity, final velocity, acceleration and time
• Inertia


  The tendency for an object's motion to stay constant unless acted on by a resultant force
• Newton's second law


  Force = mass * acceleration
• Proving Newton's second law experimentally

  1. Use a trolley on a track being pulled by a weight over a pulley

  2. Measure acceleration with light gates

  3. Plot a graph of force vs acceleration