# Section 1: Graphing Motion Review

A position-time graph plots an object's distance from a starting point (y-axis) against time (x-axis). The shape of the line tells you everything about how the object is moving. A straight diagonal line means constant speed. A flat horizontal line means the object is at rest. A steeper line means faster speed, and a gentler line means slower speed. A curved line that gets steeper indicates the object is accelerating.

The key relationship is that the slope of a position-time graph equals the object's speed. You calculate slope the same way you do in math: rise over run, which on this graph is the change in position divided by the change in time. When two objects are plotted on the same graph, the one with the steeper line is moving faster. Where the lines cross, the two objects are at the same position at the same time.

# Section 2: Forces and Newton's Laws Review

A force is a push or pull on an object, measured in newtons (N). Forces have both size and direction, making them vector quantities. When multiple forces act on an object, you combine them to find the net force. Forces in the same direction are added together. Forces in opposite directions are subtracted. If the net force is zero, the forces are balanced and the object's motion does not change. If the net force is not zero, the forces are unbalanced and the object will accelerate.

Newton's First Law (Inertia) states that an object at rest stays at rest, and an object in motion stays in motion at the same speed and direction, unless an unbalanced force acts on it. Newton's Second Law gives the mathematical relationship: F = m x a, where force equals mass times acceleration. More force produces more acceleration, and more mass means less acceleration for the same force. Newton's Third Law states that for every action force, there is an equal and opposite reaction force. These paired forces always act on different objects, which is why they do not cancel each other out.

# Section 3: Magnetism and Electricity Review

A magnet produces a magnetic field and attracts iron, nickel, and cobalt. Every magnet has a north pole and a south pole. Opposite poles attract and like poles repel. If you break a magnet in half, each piece becomes a complete magnet with both poles. Magnetic field lines run from the north pole to the south pole outside the magnet. The field is strongest at the poles, where the lines are closest together.

In 1820, Hans Christian Oersted discovered that electric current creates a magnetic field. This connection is called electromagnetism. An electromagnet is made by wrapping wire coils around an iron core and running current through the wire. Unlike a permanent magnet, an electromagnet can be turned on and off, its strength can be adjusted by changing the current, and its poles can be reversed. You can also make it stronger by adding more wire coils or using a larger iron core. Electromagnets power electric motors, generators, speakers, MRI machines, and many other devices.