chap 9 forces and energy

friction

oppresses motion between two objects in contact

elastic force

acts on stretched or compressed elastic objects to return to its original shape

non-contact force

acts on object without touching

magnetic force

exerted by magnet on magnetic objects (repel or attract)

electrostatic force

attraction/ repulsion between particles due to their electric charges

gravitational force

force of attraction between objects due to their masses

mass

amount of matter (kg)

mass

independent of gravitational field strength

mass

measured by beam balance/ electronic balance

weight

amount of gravitational force acting on object (N)

weight

dependent on gravitational field strength

weight

measured by spring balance/ weighing scale

gravitational field strength

how strong the gravitational force attracting an object with mass to earths centre is

effect of forces

changes speed of moving object

changes direction of moving object

move stationary object

stop moving object

speed

how fast an object is moving

turning effect of forces

apply force in a tool at one point to overcome force attracting another point

forces can

change size or shape (knead/mould)

change pressure on objects

pressure

amount of force acting perpendicularly on a unit area

pressure

P= force/ area

pressure in liquids

pressure higher at base

pressure in air

exerts pressure on all objects exposed to it and decreases with altitude

pressure exerted by air on earth is called atmospheric pressure

why doesn’t air pressure kill us?

air pressure outside our bodies is balanced by air pressure inside our bodies

work done (J)

energy transferred through application of force

work done

work done (J) = Force(N) x s (distance in m)

conditions for work to be done

force applied on object

object moves

object moves in same direction force is applied

energy

ability to do work

potential energy

stored energy in a system

kinetic energy

moving objects

principle of conservation of energy

energy cannot be created nor destroyed but can be converted from one form to another. The total energy in an isolated system remains constant

non renewable sources of energy

fossil fuels

renewable sources

solar energy

hydroelectric energy

wind energy

geothermal energy

nuclear energy

biofuels