Download KE = 1 2 mv2

Physical Science
Chapter 4 Notes
Section 1: Work and Machines
Work – Applying a force to make something move.
• If a force is applied and the object does not move, then no work was done.
• Equation for work:
work = force x distance, or W = Fxd
Machine – A device that helps you do work by changing the size or direction of a force.
• Machines make work easier by changing the amount of force, distance, direction, or
speed.
• Machines never reduce the amount of work; they make more work by adding friction.
• No machine is 100% effective.
Simple machine – a machine that does work with only one movement
• The six simple machines: the lever, wheel-and-axle, pulley, inclined plane (the ramp), wedge,
and screw
Compound Machine – a combination two or more simple machines
• A machine is used to change the size of a force in one of two ways: It multiplies the force, or
it multiplies the distance. A machine cannot do both
Efficiency – the ratio of output work to input work
Machines are used to make work easier. If a machine is used to multiply force it creates a
mechanical advantage.
• Mechanical Advantage - the ration of the output force to input force
• Equation for mechanical advantage:
mechanical advantage (MA) =
force output
force input
Section 2: Describing Energy
Energy – the ability to cause change.
• Energy takes many forms: mechanical, heat, light, and chemical are a few examples
System – anything around which you can imagine a boundary
Kinetic Energy – the energy an object has due to its mass and motion.
• Equation for kinetic energy:
1
Because kinetic energy
KE = mv2
2
increases in proportion to
the square of the speed, if the speed of an object is doubled its kinetic energy is quadrupled
(multiplied by 4)
Potential Energy – energy that is stored due to interactions between objects
• elastic potential energy – the energy stored by an object when it is forced into a shape that is
different from its natural shape. Examples: rubber bands, springs, vaulting poles.
• chemical potential energy - the energy stored in the chemical bonds of compounds used as
food or fuel.
• gravitational potential energy – the energy an object has when it is in an elevated position.
• Equation for gravitational potential energy: PE = mgh
•
Section 3: Conservation of Energy
Law of Conservation of Energy – energy cannot be created or destroyed
• Also known as the First Law of Thermodynamics
Mechanical Energy – the sum of the kinetic energy and potential energy of the objects in a
system
• Equations for Mechanical Energy:
ME = PE + KE
1
ME = mgh + mv2
2
Power – the rate at which energy is converted.
• Can also be defined as the rate at which work is done