physics unit 1-2

unit 1 - forces and motion

vectors

magnitude (size) + directions:
displacement, velocity, acceleration, force and momentum

scalar

magnitude (size):

distance, speed, temperature, energy, mass

resultant force

the combination of all force acted on an object

how much force is required to pull an object up?

the same size of the weight of the object (only applies to constant speed of lifting)

weight formula

weight = mass x gravity

(gravity: 9.8 N/kg on Earth)

height formulas

horizontal height:

work done = force x distance

vertical height:

gravitational potential energy = mass x gravity x height

acceleartion

the rate at which an object changes its velocity

positive acceleration

acceleration: rate of increase in velocity:

acceleration increases - speeding up at a fast pace

acceleration decrease - speeding up at a slower pace

negative acceleration

deceleration: rate of reduction in velocity

deceleration increase - slowing down at a fast pace

deceleration decrease - slowing down at a slower pace

acceleration formulas

• acceleration = initial velocity - final velocity/time

• final velocity² = initial velocity² + 2 x acceleration x displacement

types of forces

• thrust

• air resistance (drag)

• weight (gravity)

• lift

• friction

force = mass x acceleration

• predicting acceleration

• calculate forces

• determine mass

terminal velocity (full response)

• gravity pulls the object down by weight

• the object accelerates downwards initially

• air resistance (drag) increases as the speed increases

• the resultant force decreases because the upward drag acts against the downward weight

• therefore, acceleration decreases

• over time, the forces are balanced, where drag equals to weight and the resultant force becomes zero

• terminal velocity is reached and the object falls at a constant speed

stopping distance

definition: the minimum distance required to stop a vehicle

thinking distance + braking distance = stopping distance

things that affect the stopping distance

• distance (further = more time)

• reaction: drunk, tired, on drugs

• road condition (frozen? wet?)

• tire quality

• vehicle weight

work-energy theorem

formulas:

• work done = force x distance

• kinetic energy = ½ x mass x final velocity²

the work needed to stop an object equals to its kinetic energy

f x d = ½ mv²

f (friction force); d (braking distance)

hooke’s law

force = spring constant x extension of spring (F= kx)

• forces and extension are directly proportional (line at origin)

• once passed its elastic limit, the spring becomes plastic (inelastically deformed)

hooke’s law practical

1. measure extension with a ruler

2. line up 0cm of the ruler with the bottom spring, not the to avoid systematic error

3. keep an eye level when measuring to avoid parallax error

unit 2 - solid, liquid, gas

density (g/cm³)

describes how closely packed particles are OR mass per unit volume

solid, liquid, gas

solid - highly packed, high density

liquid - denser than gas, less dense than solid

gas - loosely packed, low density

measuring solids and solid

regular solids

• finding mass: use balance

• finding volume: apply “l x w x h”

irregular solids

• finding mass: use balance

• finding volume: use eureka can

liquid

• finding mass: use balance

• finding volume: find ml (ml = cm³)

heating and volumes

• decrease density

  • causing particles to expand and occupy a larger volume

• increased volume = decrease density

• decreased volume = increase density

pressure (Pa)

the force acting on a given surface area

pressure = force/area

• increased surface area = decreased pressure

• increased volume = decreased pressure

*force is concentrated when the SA or V is small

water pressure

pressure = height x density x gravity

• there are more pressure in water because liquid is denser than air

• there are higher pressure at the bottom due to gravity and weight

brownian motion

the random movement of particles suspended in liquid or gas

kinetic theory: the molecules in fluids and gas move randomly and collide with suspended objects

boyle’s law

the law states that volume and pressure are inversely proportional

(P1V1 = P2V2)

gay-lussac’s law

the law states that temperature and pressure are directly proportional

P1/T1 = P2/T2