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84 lessons · 9th Grade
Newton's first law states that an object at rest stays at rest and an object in motion stays in motion unless acted on by an unbalanced force. This is called inertia.
Newton's second law says that force equals mass times acceleration (F = ma). A heavier object needs more force to accelerate at the same rate as a lighter one.
Newton's third law states that for every action there is an equal and opposite reaction. When you push against a wall, the wall pushes back on you with the same force.
Gravity is the force that pulls objects toward each other. On Earth, gravity pulls everything toward the center of the planet, giving objects their weight.
Friction is a force that opposes motion between surfaces that touch. Rough surfaces create more friction than smooth ones. Without friction, you could not walk or grip objects.
Simple machines make work easier by changing the direction or amount of force needed. The six simple machines are lever, pulley, inclined plane, wedge, screw, and wheel and axle.
Electricity flows through circuits. A simple circuit needs a power source, a conductor (wire), and a load (like a light bulb). Breaking the circuit stops the flow of electricity.
Electromagnets are temporary magnets created by running electricity through a coiled wire. They can be turned on and off and are used in motors, speakers, and MRI machines.
Kinetic energy is the energy of motion. A moving car, a rolling ball, and a flying bird all have kinetic energy. The faster an object moves, the more kinetic energy it has.
Potential energy is stored energy based on position or condition. A ball at the top of a hill has gravitational potential energy. A stretched rubber band has elastic potential energy.
Magnets have north and south poles. Opposite poles attract and like poles repel. The magnetic field is strongest at the poles and gets weaker with distance.
Static electricity builds up when objects gain or lose electrons through rubbing. Rubbing a balloon on your hair transfers electrons, making the balloon stick to a wall.
Energy can be transformed from one form to another but cannot be created or destroyed. A light bulb converts electrical energy into light and heat energy.
Renewable energy sources like solar, wind, and hydroelectric power can be replenished naturally. Nonrenewable sources like fossil fuels take millions of years to form.
Speed measures how fast an object moves (distance divided by time). Velocity includes both speed and direction. An object changing direction is accelerating even at constant speed.
Momentum is mass times velocity. A heavy truck moving slowly can have the same momentum as a light car moving fast. Momentum is conserved in collisions.
Work in science means using a force to move an object a distance. If you push a box across the floor, you do work. If you push a wall and it doesn't move, no work is done.
Balanced forces are equal in size and opposite in direction, so an object stays still or moves at constant speed. Unbalanced forces cause an object to accelerate or change direction.
A force is a push or pull that can change an object's motion, shape, or direction. Forces are measured in Newtons and can act through contact or at a distance.
A lever is a rigid bar that rotates around a fixed point called a fulcrum. Seesaws, scissors, and bottle openers are all examples of levers that multiply force.
