Physics - P1 Motion, Forces and Energy

Physical quantities and measurement techniques - doesn't have graphs

Newton’s Law of Gravity:

F = G m1m2/r2

to measure small lengths

either measure multiple to find the average or use a specialized tool such as a micrometer or vernier caliper

1 ml =

1 cm3

volume of cylinder

pi radius squared times height

to measure the volume of an irregular object

displacement method

Period (time for one oscillation)

measure multiple oscillations and find the average

mass (m)

the amount of matter in an object, units kg

weight (w)

the force of gravity on an object in a gravitational field, units Newtons (N)

g =

gravitational field strength, force per unit mass (N/kg). At earth’s surface, g = 9.8 N/kg

w=

w=mg

what does a balance measure?

weight but displays mass (because g is known)

density (ρ)

mass per unit volume, units kg/m3

density=

mass/volume

scalar quantity has

vector quantity

magnitude and direction

scalar examples

distance, speed, time, mass, energy and temperature

vector examples

distance, speed, time, mass, energy and temperature

speed

distance travelled per unit time

speed =

v = s/t

average speed=

total distance travelled/total time taken

velocity

speed in a given direction

acceleration

change in velocity per unit time

an object moving with increasing speed is…

accelerating

an object moving with decreasing speed is

decelerating

deceleration

a negative acceleration

that the acceleration of free fall g for an object near to the surface of the Earth is approximately constant and is approximately…

9.8 m/ s^2

gravitational field strength is equivalent to

the acceleration of free fall

friction

force that resists sliding between two surfaces; results in heating

air resistance

force that resists an object’s motion through air (friction in gas)

elastic

force that restores an object to its original shape

Hooke’s Law of springs

the extension of a spring is proportional to the force applied

F=

kx

Newton's second law of motion states

F = ma, or when there is a resultant force on an object it will accelerate in the direction of the force.

the resultant force and the acceleration

are in the same direction

resultant force

the sum of two or more forces acting on an

object

Forces in the same direction

are added

Forces in opposite directions

are subtracted

force (F)

a push or pull between two objects, units Newtons

Forces can change the

size, shape or motion of an object

moment =

force × perpendicular distance from the pivot

when there is no resultant force and no resultant moment…

an object is in equilibrium

Pressure (p) =

force/area

state that energy may be stored as

kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal)

equilibrium

no resultant force and no resultant moment; motion does not change

principle of moments

If a system is in equilibrium, the sum of the anticlockwise moments about a turning point equals the sum of the clockwise moments

Centre of Mass (CM)

the centre of an object’s mass distribution

• An object acts as if its entire weight acts at the centre of mass

• A system is stable when its CM is directly above or below the base

equation for kinetic energy

Ek= 1/2 mv^2

the equation for the change in gravitational potential energy

change in x Ep = mg x change in h

mechanical or electrical work done is equal to

the energy transferred

radiation from the Sun is the main source of energy for all our energy resources

except geothermal, nuclear and tidal

efficiency

• efficiency = useful energy output/total energy input

  × 100%

• efficiency = useful power output/total power input

  × 100%

energy is released by nuclear fusion in the Sun

energy is released by nuclear fission in nuclear reactors

power (p)

work done per unit time and also as energy transferred per unit time

power (p) equation

P = W/t

P = change in E/t