Applications of Newton’s Laws

APPLICATIONS OF NEWTON’S LAWS

There are several situations that involve an application of Newton’s Laws. The topic that comes up in looking at these laws is called “drag force”. Consider two tugboats pushing a boat in the x and y directions at different rates of force. This is seen in figure 17:

Figure 17.

The question is, what is the drag force on the boat? This is the force of the boat that is resisting motion, which will be an opposite force to the direction of the way that the boat is being pushed. It is a frictional force exerted by fluids like air or water. The force will be the sum of the x force and the y force, with the drag force being an opposite force in magnitude and direction to the final force on the boat.

In this case, the “applied” or final force will be the square root of the x force squared plus the y force squared (from the Pythagorean theorem) and the angle theta will be the negative one tangent of the y force divided by the x force. The net force is the applied force minus the drag force. If you know the mass of the boat and its acceleration, you can determine the drag force. We will talk more about this in a minute. Suffice it to say that the drag force will not be the same as the applied force as long as the boat is moving anywhere in the direction of the applied force.