Force and Motion

Unit Review Sheet

Facts and Definitions

Lesson 1: Force

• A force is a simple push or pull.
• A contact force is a force in which the object doing the pushing or pulling has to physically touch the thing being pushed or pulled.
• A noncontact force is a force that does not involve any physical contact between objects.
• Gravity is a noncontact force that pulls any two objects with mass toward each other.
• Applied force is a force that is applied to an object by something else.
• Normal force is the force that two objects exert on each other when they are touching; it is the reason objects feel solid.
• Tension force is a force that is applied to an object by something else through anything that resembles a string: ribbons, thread, straps, cables, wires, chains.
• Friction is a force that occurs when two objects slide across each other; friction slows moving objects down and makes it harder for objects at rest to start moving.
• Air resistance is the frictional force an object experiences when it moves through air.
• Electromagnetism is a noncontact force between particles that have a charge (like protons and electrons); static electricity and magnetism are two examples of this force.
• Strong nuclear force keeps protons and neutrons together in an atom's nucleus.
• Weak nuclear force allows protons and neutrons to change into each other, so that an atom of one element can turn into a different element; without this force our Sun wouldn't burn (it creates heat by changing atoms of hydrogen into atoms of helium), and we wouldn't have nuclear power plants.

Lesson 2: Newton's Laws of Motion

• Motion is a change in the position of an object with respect to time.
• Newton's laws of motion explain how forces are related to the motion of objects.
• Newton's first law: an object at rest tends to remain at rest, and an object in motion tends to remain in motion, unless acted upon by some force.
• Inertia is the tendency of objects to remain at rest, or for objects in motion to remain in motion, unless acted upon by some force.
• Equilibrium is the state of an object when all the forces acting on it are balanced.
• Balanced forces are two or more forces applied to an object in opposite directions that are equal in magnitude (size). Balanced forces keep objects at rest or keep them moving at the same speed in the same direction.
• Newton's second law: the acceleration of an object is proportional to the amount of unbalanced force acting on it; or, force equals mass times acceleration.
• Mass is the amount of matter in an object.
• Velocity is the rate of change of the position (distance) of an object over time.
• Acceleration is a change in the velocity of an object over time.
• Newton's third law: if object A pushes on object B, then object B pushes on object A with an equal amount of force, but in the opposite direction.

Lesson 3: Graphing Motion

• Constant refers to a uniform direction, speed, or velocity or to a force that does not change.
• Deceleration is a decrease in the velocity of an object over time, or a negative acceleration.
• Irregular is the opposite of constant; it is when direction, speed, velocity, or force changes or is not uniform.

Lesson 4: Speed, Velocity, and Acceleration

• Remember that velocity is the rate of change of the position (distance) of an object over time, and acceleration is the rate of change of the velocity of an object with respect to time.

Lesson 5: Centripetal Force and Terminal Velocity

• Centripetal force is an inward force that pulls or pushes an object towards the center of rotation.
• Centrifugal force is an outward force that pushes or pulls an object away from the center of rotation.
• A frame of reference is a location or point of view.
• Terminal velocity is the greatest velocity a falling object can reach. When an object reaches its terminal velocity, the forces on it are balanced, and it is at equilibrium.

Lesson 6: Work

• The newton (N) is a unit of measure of force representing a combination of acceleration and mass (kg × m/s²).
• Work is the amount of energy transferred by a force acting through a distance in the direction of the force.
• A joule is the unit of measure for work. One joule (J) is how much work is done when a force of one newton moves an object one meter. (1 J = 1 N × m, or J = Nm)
• Kinetic energy is the energy of matter in motion.
• Stored energy is called potential energy.
• Simple machines are mechanical devices that change the direction or magnitude of a force.
• Magnitude is a term used to describe the size or amount, usually of a force.
• Mechanical advantage is a measure of how much a simple machine increases the force applied to it. (MA = output force/input force)

Lesson 7: Newton in the Milky Way

• Johannes Kepler's laws of planetary motion explain the movement of orbiting objects.
• Kepler's first law of planetary motion: Planets orbit the Sun in an ellipse.
• Kepler's second law of planetary motion: As a planet comes closer to the Sun during its orbit, the planet speeds up. As it moves away from the Sun, it slows down.
• Kepler's third law of planetary motion: Planets farther from the Sun have a larger and slower orbit than planets closer to the Sun.

Final Project: Demonstrating Newton's Laws

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