Unit 02 -- Forces and Changing Motion

Vocabulary

1. Acceleration -- a change in the velocity of an object. Because it is a change in the velocity, it could mean speeding up, slowing down or changing direction. It is a vector quantity. It is symbolized with a lowercase a. Its units are m/s/s, read "meters per second per second."
2. Gravitational Acceleration -- the acceleration applied to objects by the gravitational pull of the Earth. At the Earth's surface, it is about 9.81 m/s/s for all objects, regardless of their weight. It is symbolized with a lowercase g.
3. Free Fall -- the state in which an object's motion is changing due only to gravitational acceleration.
4. Resistance Forces -- forces that always act in the opposite direction of the motion of the object.
5. Friction -- a resistance force due to the rubbing of surfaces as objects slide past. Unlike other forces, it is often symbolized with a lowercase f.
6. Air Resistance -- a resistance force due to the object's collisions with air particles. It is also called drag.
7. Mass -- the amount of matter in an object. In physics, it has two consequences: (1) it determines the amount of resistance to changes in motion for an object, and (2) it produces and interacts with gravitational fields.
8. Kilograms -- the standard MKS unit of mass. It is abbreviated with a kg.
9. Weight -- a measure of the gravitational pull of the Earth on an object. The more mass an object has, the more it interacts with the Earth's gravitational field, and, therefore, the more it weighs.
10. MKS System of Units -- the subset of metric system units that are most commonly used in physics. The M stands for the meter -- the standard for length measurement. The K stands for the kilogram -- the standard unit for mass. The S stands for seconds -- the standard unit for time.
11. Newtons -- the common unit of all force measurements in the MKS system of units. It is abbreviated with an N or sometimes an n. It is equivalent to the force required to provide a 1 kilogram mass with an acceleration of 1 m/s/s, i.e. 1 N = 1 kg * m/s/s.
12. Spring Scale -- a measurement device used to judge the size of a force. The longer the spring stretches, the larger the force must be.
13. Newton's Second Law of Motion -- It states, "the acceleration of an object is directly proportional to the net force acting on the object, is inversely proportional to the mass of the object, and is in the direction of the net force." More simply stated, a net force causes a mass to accelerate. The more net force applied, the more it will accelerate. The more mass on which the net force is applied, the less acceleration is produced.
14. Terminal Speed -- the speed at which the upward force of air resistance balances out the downward force of the Earth's gravitational pull. Since there is no longer any net force at this speed, the speed is constant.
15. Terminal Velocity -- the terminal speed, but with the direction given as well.

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