Forces

• 5 Forces


  • Contact
  • Non-contact
• Contact


  Something being physically pushed or pulled, friction air resistance or tension
• Non-contact


  Not touching it, such as gravity and magnetism
• Basics of motion


  • Speed
  • Velocity
  • Displacement
  • Acceleration
  • Circular path
• Speed


  A scalar quantity used to measure motion, they only have a magnitude and no direction
• Distance


  A scalar quantity as it only has a magnitude
• Velocity


  Describes an object's direction as well as its speed, it is a vector as it has a magnitude and a direction
• Displacement


  The distance an object moves in a straight line from a starting point to a finishing point, is a vector
• Acceleration


  Equal to the change in velocity/time taken
• Circular path


  Objects have a constant speed but have a positive acceleration due to their direction constantly changing
• Quantities


  • Scalar
  • Vector
• Scalar


  Magnitude no direction, such as speed, distance, mass
• Vector


  Both a magnitude and a vector, such as displacement and velocity
• Spring


  An object can be deformed with a force, spring constant is N/m
• Moment


  A turning force, it is the force times the distance from pivot
• Gears


  A small gear can turn a large gear to increase the moment produced from it
• Mass and weight


  • Mass
  • Weight
  • Centre of mass
  • Inertia
• Mass


  Of an object is a measure of the amount of matter it contains, it is constant
• Weight


  Of an object can be measured using digital balances, they use w = mg to convert weight into mass because earth's gravity is constant
• Centre of mass


  Mass is spread around the body, but the center of mass is where all the mass appears to be. The center of mass will be directly below where an object is hung from
• Inertia


  An object's mass is measured on how hard it is to change its motion. An object with a high mass has a higher inertia since it is difficult to move, this makes its motion hard to stop
• Resultant forces


  The sum of all forces acting on an object. The change in motion is caused by a resultant force
• Force diagrams


  Show all the forces acting on an object, the velocity of each force is shown through the direction of the arrows, and how long they are. We can use it to see the direction of an object based of their resultant force
• Newton's Laws


  • First law
  • Second law
  • Third law
• Newton's first law


  Velocity of an object will only change if a resultant force is acting on the object, this applies to a stationary or moving object - inertia
• Newton's second law


  Resultant force = mass X acceleration
• Newton's third law


  Whenever two objects interact, the forces that they exert on each other are equal and opposite – if a person sits on a chair, the chair must push back on the person's body with an equal force, but opposite direction
• Stopping distance of a car

  Resultant of the thinking distance and the braking distance
• Speed increases


  Stopping distance increases, doubling speed quadruples it
• Thinking distance


  Affected by drugs or tiredness
• Stretching a spring


  We can stretch bend or compress objects through applying a force, for this to happen there must be 2 or more forces acting on an object. If one force is acting, then we can bend a spring
• Deformation


  • Inelastic
  • Elastic
• Inelastic deformation


  The object will not return to its original shape, like a car after a crash
• Elastic deformation


  The object will return to its original shape, such as a spring
• Hooke's law


  The force = spring constant X extension
• Limit of proportionality


  This is where Hooke's law does not apply, typically were the elastic limit is met
• Practical - measuring spring extension

  Set up the ruler and the spring, load on weight and measure the size of the spring, minus this from the starting point. Force is on the X axis, extension is on the Y axis
• Elastic potential energy


  Work done on a spring- when we compress a spring, the EPE is stored in the string, this is equal to the work done when stretching it
• Acceleration


  • Free fall
  • With air resistance
  • Terminal velocity
• Free fall


  Acceleration due to gravity and will accelerate at a constant rate, it would have a straight line with a constant slope on a speed time graph, but curved on a distance time graph