Definition: The ability of an object to do work.
Unit: Joules
Types of Energy:
Mechanical: Energy of Movement and Position.
Chemical: Energy stored in chemical bonds of molecules.
Thermal: Heat energy.
Nuclear: Energy produced from the splitting of atoms.
Radiant: Energy in the form of electromagnetic waves.
Electric: Energy traveling as the flow of charged particles (electrons).
Definition: Work is done when a task produces a change in energy.
Factors that affect work: Force and Distance.
Formula: W = Fd ( \text{Note: work requires a distance!} )
Example problems:
To lift an object 2m high using 5N of force: 10 Joules.
Pushing a stationary wall with a force of 1000 N: 0 Joules (no movement).
Definition: How much work is performed over a certain amount of time.
Formula: P = W/T
Unit: Watts (W).
Horsepower:
1 hp = 746 Watts
1 horsepower = the output of a farm horse.
Common items converted to horsepower:
Coffee maker: 0.75 hp
Blender: 1.5 hp
Lawn mower: 5-6 hp
Corvette: 400+ hp
Example problem:
Superman, at 90kg, jumps a 40m building: 35,280 Joules of work in 3s gives a power output of 71,760 Watts.
The amount of work done by an object does not depend on the path taken.
Work on an object gives it the opportunity to do work (e.g., winding a toy).
Definition: Energy of movement and position.
Potential Energy:
Energy of Position.
Gravitational Potential Energy: due to elevated positions.
Formula: PE = mgh
Kinetic Energy:
Energy of Motion.
Formula: KE = 1/2mv². Note: Velocity is squared.
Energy Conservation:
Energy is constantly transforming but never disappears.
Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.
PE = KE in a system.
On a roller coaster:
Greatest PE at A, lowest at B.
Greatest KE at B, lowest at A.
Jill: Velocity 5m/s, mass 60kg: Kinetic Energy = 752J.
Bob: Mass 70kg, height 13m: Potential Energy = 8,918J.
Definition: The amount of force applied to a spring is proportional to the amount it’s stretched or compressed.
Formula: F = kx.
Definition: Momentum is a measure of the quantity of motion an object possesses.
Formula: [ P = m \times v ]
Where:
P is momentum (symbolized as (P))
m is the mass of the object
v is the velocity of the object
Units: Momentum is expressed in kg·m/s.
Standard units and Letter abbreviation:
Standard unit | Letter Abbreviation (in a formula) | |
mass | kg | m |
momentum | kgm/s | P |
Velocity | m/s | v |
Kinetic energy | J | KE |
Spring constant | N/m | K |
Power | W | P |
Work | J | W |