Physics-unit 5 

A force is a push or pull that acts on an object.

==CONTACT FORCES:==

  • air resistance- acts on anything moving through air, slowing it down
  • friction- acts against anything moving slowing it down
  • tension-acts when an object is pulled in opposite directions
  • thrust- acts on object with an engine. e.g. planes, cars
  • normal contact force-keeps objects resting on surface
  • upthrust-keeps objects afloat
  • lift-keeps flying objects in air

==NON-CONTACT FOCES:==

  • electrostatic force-acts between charged objects. attracting/repelling them.
  • magnetic force: acts between magnets and other magnetic materials.
  • gravitational force (weight)-pulls things down to the centre of the earth

weight vs mass

Mass-the amount of stuff an object contains (in kg)

%%weight (N)= gravitational field strength (N/kg) x mass (kg)%%

%%W=GM%%

weight is directly proportional to mass.

weight is directly proportional to gravitational field strength

HOOKES LAW:

to change the shape of an object two forces are applied in opposite directions

Tension-acts when an object is pulled in opposite directions ,away from each other

Compression- acts when an object is pulled in opposite directions ,towards each other

behaviour of a spring:

elastic deformation- occurs when an object can return to it’s original shape after being stretched

inelastic deformation: occurs when an object cannot return to it’s original shape after being stretched

Initially as you increase the force on a spring the force and extension are directly proportional as they increase at the same rate and during this time the spring is elastically deforming because it will return to it’s original shape when the force is removed. However if you continue to increase the force eventually the extension and force stop increasing at the same rate and therefore is no longer directly proportional so the spring is inelastically deforming because when the force is removed the spring will no longer return to it’s original shape.

Practicle:

IV: force applied to the spring

DV: the extension of the spring

CV: spring, ruler

  1. hang the spring from a clamp stand and use a g-clamp to clamp the stand to the table
  2. measure the initial length of the spring using a ruler
  3. add 100g mass (force of 1N)
  4. wait for the spring to stop oscillating and measure the final length of the spring
  5. calculate the extension of the spring(final length - initial length)
  6. repeat adding 100g (force-1N) each time until you reach 5N

Hazard: spring

Risk :flying loose and hitting eye

Control: wear googles

^^HOOKES LAW: the force on a spring is directly proportional to the extension provided the elastic limit is not exceeded^^