forces (paper 2 physics)

• a force is a push or pull that acts on an object due to its interaction with another object
• forces are classed as vector quantities
• vector has both direction and magnitude
• contact- objects that are physically touching
• non contact- doesn't require for the objects to be touching
• contact forces:

  • tension
  • air resistance
  • friction
  • normal contact force (reaction force)
• non-contact force:

  • gravitational
  • magnetic
  • electrostatic
• in a non contact force the strength of the object decreases as the object moves further away
• air resistance is a contact force because of the physical contact (collisions) between an object and the particles in the air.
• scalar- has only magnitude and has no direction
• scalar examples:

  • speed
  • distance
  • mass
  • temperature
  • time
• vector examples:

  • velocity
  • displacement
  • acceleration
  • momentum
  • force
• A women walks 500 m from her home to the shop. She then walks 200 m to the park and finally 400 m back to her home. What is the overall distance and displacement of her journey? 

  distance = 1100

  displacement = 0
• free body diagrams are used to show the forces acting on an object
• 2 properties that might affect resultant force:

  • direction
  • mass
• if all forces in an object balance out then we say the object is in equilibrium
• if an object returns to its original shape after forces have been removed then it is known as elastic deformation
• if an object does not return to its original shape after the force is removed, it is inelastic deformation
• applying forces to an object can cause it to:

  • stretch
  • bend
  • compress
• Extension is the increase in length of a spring when its stretched
• minimum number of forces required to stretch, compress or bend an object is 2
• An object's spring constant is a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre. (N/m)
• high spring constant means that it requires more energy to stretch it.
• Hooke's Law states that the extension of an object is directly proportional to the force applied.
• A= elastic deformation

  B= elastic limit

  C= inelastic deformation

  
• hookes law formula= F=ke
• Every spring has a characteristic called the spring constant, which is a measure of how firm the spring is.

  A higher spring constant means the spring is more firm.

  A lower spring constant means the spring is less firm.
• A spring has a spring constant of 120 N/m, and an unstretched length of 0.5m.

  What force is required to stretch the spring from 0.5m, to 0.6m?

  =12 N
• A force of 5 N is applied to a spring, causing it to stretch from a length of 0.1 m, to a length of 0.15 m.

  What is the spring constant of the spring?

  = 100 N/m
• A spring with a spring constant of 4 N/m is stretched by 0.5 m.

  How much elastic potential energy did it gain?

  = 0.5 J
• 8 J of energy is used to stretch a spring by 0.1 m.

  What is the value of its spring constant?

  = 1600 N/m
• • the gradient of the straight part of the graph tells us the spring constant
  • the area under the curve tells us the elastic potential energy
  • The point where the line goes from straight to curved is referred to as the: elastic limit or limit of proportionality