#NEWTON UNIT EXAMPLES PLUS#

For a sphere or disk made of homogenous material, this point is of course at the center. For example, in a rigid object, this center of mass is the point where the object will stay balanced even if only supported at this point. The point we choose for this is the point about which the system’s mass is evenly distributed. When we describe the acceleration of a system, we are modeling the system as a single point which contains all of the mass of that system. This concept will be revisited many times on our journey through physics.

The concept of a system is fundamental to many areas of physics, as is the correct application of Newton’s laws. Sometimes the system is obvious, whereas other times identifying the boundaries of a system is more subtle. You must define the boundaries of the system before you can determine which forces are external. The internal forces actually cancel, as we shall see in the next section. Only external forces affect the motion of a system, according to Newton’s first law. Again looking at Figure 4.5(a), the force the child in the wagon exerts to hang onto the wagon is an internal force between elements of the system of interest. An internal force acts between elements of the system. The two forces exerted by the other children are external forces.

#NEWTON UNIT EXAMPLES PLUS#

For example, in Figure 4.5(a) the system of interest is the wagon plus the child in it. What do we mean by an external force? An intuitive notion of external is correct-an external force acts from outside the system of interest. Newton’s first law says that a net external force causes a change in motion thus, we see that a net external force causes acceleration.Īnother question immediately arises. A change in velocity means, by definition, that there is an acceleration. Before we can write down Newton’s second law as a simple equation giving the exact relationship of force, mass, and acceleration, we need to sharpen some ideas that have already been mentioned.įirst, what do we mean by a change in motion? The answer is that a change in motion is equivalent to a change in velocity. Newton’s second law of motion is more quantitative and is used extensively to calculate what happens in situations involving a force. It mathematically states the cause and effect relationship between force and changes in motion. Newton’s second law of motion is closely related to Newton’s first law of motion.

Apply Newton’s second law to determine the weight of an object.

Understand Newton’s second law of motion.

Define net force, external force, and system.

By the end of this section, you will be able to do the following:

Newton unit examples