Contemporary's GED Science
(See pages 289–291)
Physics is the study of energy in all its forms:
Laws of Motion
(See pages 292–298)
One of the great advances in science occurred during the 1600s when Isaac Newton discovered natural laws that govern the motion of objects:
- The Law of Inertia: If no force is applied, an object at rest will remain at rest, and an object in motion will move in a straight line at constant speed.
- The Law of Acceleration, Part I: An object's speed increases in proportion to the amount of force applied.
- The Law of Acceleration, Part 2: For the same amount of applied force, a lighter object accelerates—changes its speed—at a greater rate than a heavier object.
- The Law of Interaction: For every action, there is an equal and opposite reaction.
Newton used his laws of motion to discover the Law of Universal Gravitation:
- Part 1: Gravitational force is an attractive force, a force that pulls two objects toward one another.
- Part 2: Gravitational force is greater for heavy objects (objects with more mass) than for light objects.
- Part 3: The force of gravity decreases as the distance between objects increases.
Force, Work, and Machines
(See pages 299–304)
Scientists define work as the product of the units of force times the units of distance. For work to occur, there must be force applied to an object and the object must move:
Machines are devices that are designed to make work easier.
A lever is a simple machine that consists of a bar that moves around a pivot point called a fulcrum. A lever changes a small prying force into a much larger one.
A wheel and axle is a simple machine that changes a small turning force into a much larger one.
Law of Conservation of Energy: During interactions, energy may change from one form to another, but no energy is lost. The total amount of energy present remains constant.
- Kinetic energy—energy of motion
- Potential energy—stored energy
Friction is a force that either slows a moving object or prevents a nonmoving object from being moved:
Sliding friction—friction felt when one object rubs against another
Rolling friction—friction felt when an object is placed on wheels and moved
Fluid friction—friction felt when an object moves through a fluid, such as water or air
Static friction—friction felt when a force is applied to an object that doesn't move