chapter 9 - forces and transfer of energy

Front

what are the type of forces?

Back

1. 1. forces acting between two objects in physical contact are called contact forces, e.g. friction, elastic force

2. 2. forces acting between two objects that are not touching each other are called non-contact forces e.g. gravitational force, magnetic force

Front

contact forces

Back

1. 1. friction - is the force that opposes motion between two surfaces in contact

2. 2. elastic force - is the force acting on a stretched or compressed elastic object to return to its original shape

Front

non-contact forces

Back

1. 1.gravitational force- force that attracts two objects towards each other; when a planet exerts gravitational force on an object and pulls it towards the center, the object is known to have weight

2. 2.magnetic force- force exerted between a magnet and another magnetic material such as iron or steel; magnetic force also exists between two magnets; when unlike poles are brought together

Front

comparing weight and mass

Back

weight - is the measure of the gravitational force acting on an object

weight = force

SI unit of force, newton (N) = SI unit of weight, newton (N)

mass - amount of matter in an object

SI unit of mass = kilogram

*mass remains the same regardless of the location

*the weight of an object may change with its location if the gravitational force exerting on it changes

Front

formula for weight

Back

weight = mass X gravitational force

W=MG

Front

what happens when two or more objects interact?

Back

changes due to the turning effect of a force on an object - a force applied on an object can cause a turning effect about a fixed point called the pivot

changes in size and or/ shape of an object - when a force exerted causes the transfer on energy between objects, the size and or shape of the object may change

changes in pressure on an object - pressure is an effect of force acting on an object; area of contact affects the pressure exerted by an object

Front

pressure

Back

pin vs cork - the pin, which has a very small area of contact, exerts a very high pressure on the cork board thus it can be pushed into the cork board easily

definition : force per unit area

formula : pressure = force/area

SI unit of pressure is pascal (pa)

Front

transfer of energy due to its application of forces

Back

• - a force applied causes an object to move in the same direction as the force

• SI unit for energy is joule (j)

• ✓A force is applied on the object 

  ✓The object moves 

  ✓The object moves in the same direction as the force applied on it 

  —> then only work is done 

Front

formulas

Back

weight - W=MG

pressure - P=F/A

work done- work done = force X distance

kinetic energy- KE= 1/2massvelocity2; ½mv²

gravitational potential energy- PE = mgh (mass, gravity, height)