AP Physics Chapter 9

Energy

The capacity to do work or produce change, observed indirectly through its effects

Key characteristics of energy

Transferable (energy moves from one place to another) and transformable (energy changes from one form to another)

How is energy related to work?

Involves the transfer or transformation of energy

Formula for work

W = Fd

When is work done?

When a force acts on an object, and the object moves in the direction of the force

Unit of work

Joule

Power

The rate at which work is done, calculated by the formula: Power = Work Done / Time Interval

SI Unit of Power

Watt or Joule per second

Mechanical Energy

THe energy due to the position or movement of an object, including kinetic and potential energy

Examples of potential energy

Elastic potential energy, chemical energy, gravitational potential energy

Formula for gravitational potential energy

PE = mgh

Kinetic energy

The energy of motion, dependent on an objects mass and speed. Formula: KE = 1/2mv²

Work-Kinetic Energy Theorem

The work done on an object equals the change in its kinetic energy: Fd=1/2mv²

Law of Conservation of Energy

Energy cannot be created or destroyed; it can only be transformed from one form to another, but the total energy remains constant

How do machines work?

Machines multiply forces or change the direction of forces while conserving energy (energy input = energy output)

Mechanical advantage

The ratio of output force to input force, or input distance to output distance

Types of levers

Type 1 Lever: Fulcrum between input force and load

Type 2 Lever: Load between fulcrum and input force

Type 3 Lever: Input force between fulcrum and load

Efficiency formula

Efficiency = (Useful Work Output / Total Work Input) x 100%

Why can’t machines achieve 100% efficiency?

Due to energy losses, mostly as heat, caused by friction or molecular motion

Energy degradation

Energy is not destroyed but eventually converted into thermal energy, which is less useful