| A | B |
|---|
| Force. | a push or a pull. See Figure 1. |
| Net force. | combination of all forces acting on an object. |
| Balanced forces. | two or more forces whose effects cancel each other out, do not change the motion of an object. |
| Unbalanced forces. | two or more forces acting on an object that do not cancel, and cause the object to accelerate. |
| Newton's first law of motion | states that if the net force acting on an object is zero, the object will remain at rest or move in a straight line with a constant speed. |
| Friction. | force that acts to oppose sliding between two surfaces that are touching. |
| Newton's second law of motion | states that an object acted upon by a net force will accelerate in the direction of the force, and that acceleration equals the net force divided by the object's mass |
| Weight. | gravitational force between an object and Earth. |
| Center of mass. | point in a object that moves as if all of the object's mass were concentrated at that point. |
| Newton's third law of motion | states that forces always act in equal but opposite pairs. |
| Explain the differences between force, inertia, and weight. | force is a push or a pull; inertia is resistance to change in motion; and weight is a force due to gravity. |
| Compare Newton's first law of motion and Newton's third law of motion. | Newton's first law is that a body has inertia; Newton's third law is for every force there is an equal and opposite force. |
| Compare friction and force. | Friction is a type of force. |
| Compare net force and balanced forces. | Net force is concerned with the total of all forces on an object. Balanced forces means the net force equals zero. |
| Compare balanced forces and unbalanced forces. | with balanced forces an object does not accelerate; with unbalanced forces an object accelerates. |
| Compare friction and weight. | friction includes opposing forces and weight is a force due to gravity. |
| Compare Newton's first law of motion and Newton's second law of motion. | In Newton's first law of motion a body has inertia; in Newton's second law a = F/m. |
| Compare friction and an unbalanced force | friction is opposing force and with unbalanced force an object accelerates. |
| Compare net force and Newton's third law of motion. | The net force is the sum of forces; Newton's third law is that for every force there is an equal and opposite force. |
| What is one thing that changes when an unbalanced force acts on an object? | motion |
| What force slows a book sliding on a table? | sliding friction |
| If two students are pushing on the left side of a box with a total force of 20 N and another student is pushing on the other side of the box with a total force of 25 N which way will the box move? | Left |
| What combination of units is equivalent to the Newton? | one kilogram times meters per second squared (1 kg.m/s2) Where the mass of an object is given in kilograms and the acceleration is given in meters per second squared. |
| An object is accelerated by a net force in the direction of ... | the force |
| You are riding your bike. When are the forces acting on your bike in balance? | when you are pedaling at a constant speed. |
| Which of the following has no direction? a. force b. acceleration c. weight d. mass | mass has no direction |
| Explain why the speed of a sled increases as is moves down a snow-covered hill, even though no one is pushing on the sled. | acceleration due to gravity increases speed. |
| A baseball is pitched east at a speed of 40 km/h. The batter hits it west at a speed of 40 km/h. Did the ball accelerate? | Yes, the ball changed direction. |
| Frequently, the pair of forces acting between two objects are not noticed because one of the objects is Earth. Explain why the force acting on Earth isn't noticed. | The Earth is so massive, the forces people exert on it cause very little acceleration. |
| Velocity. | the speed and direction of a moving object. |
| Acceleration. | the change in velocity divides by the time over which the change occurred. |
