physics unit 3-4

unit 3 - electricity

electric circuit

current travels from + to -

types of resistance

• resistor: has a resistance that does not change

• variable resistor: has a slider that control and changes the resistance

• thermistor: a temperature-dependant resistor

• LED: a light-dependant resistor

• diode: a resistor that only allows currents to flow in one direction

rule for resistance

unit 4 - energy

energy is never added, it is only transferred

types of energy

• chemical

• thermal

• kinetic

• electrostatic

• magnetic

• atomic

• elastic

• gravitational potential

*they are transferred by: heat, radiation, electrically, mechanically

work done (joules)

the amount of energy transferred when a force moves an object

work done = force x distance

sankey diagram

loss of GPE = gain in kinetic energy

kinetic energy = ½ mv²

GPE = m x g x h

when asked about speed/height in falling/rising object:

½ mv² = mgh

energy transfer in a book

at the top: the book has maximum GPE and zero kinetic energy (since it is stationary)

falling:

• as the book accelerates downwards, the height decreases, loosing GPE

• the velocity increases, causing it to gain kinetic energy

at the bottom: the book reaches maximum speed. At this moment, GPE is zero, meaning that all of the initial GPE has been transferred to kinetic energy

*maximum speed = maximum kinetic energy

power (watt)

energy moved from plug socket to phone:

power = energy transferred / time

pushing a car:

power = work done / time

conduction

the transfer of thermal energy through a substance

conduction process

1. the metal bar is heated

2. this causes the particles to vibrate

3. the vibration is spreaded throughout the metal bar

4. the whole metal bar is heated

convection

the flow of heat energy from a region of high temperature to a region of low temperature through the movement of fluid

convection process

1. the fluid near the heat source gains thermal energy and expands

2. because it is expanded, the heated fluid becomes less dense

3. they are less dense than the cooler surrounding fluid, causing them to float

4. the cooler surrounding fluid sinks and takes its place, creating a convection current.

radiation

the transfer of heat energy from a region of high temperature to a region of low temperature by infrared radiation

• takes place without any particles

• absorbing radiation: heats up and the temperature will rise