What is fnet equal to

These are usually the x-direction side. For now we are only going to take into account these two. In the diagram above we can see the two axis, x and y. From this picture all three forces are exactly. This means either the force is all in the x-direction or all in the y-direction. From this we will get the two following equations;. From this we can than determine the acceleration of the object in the x-direction and also then in the.

Using common sense though we can also see that the accelerating in the y-direction is going to be. This law is very useful in the fact we can determine the acceleration of an object if we know the forces. We expect this mass to have an acceleration a that is up. There are no horizontal forces. This one equation has two unknowns -- tension T and acceleration a. So we need more inormation. We expect this mass to have an acceleration a that is down.

We can choose to call down "positive" for this mass or we can call up "positive" and then we expect this mass to have an acceleration of - a. Either choice is fine.

Of course, this one equation also has two unknowns -- tension T and acceleration a. But now we have two equations with two unknowns and that is sufficient. We can solve for the tension T in the first equation,. Example 6: Now, let's consider an inclined Atwoods machine. Masses m 1 and m 2 are connected by a string which runs over a pulley and mass m 2 sits on a smooth inclined plane. Remember, "smooth" is just a code word for "frictionless"; we'll get to friction shortly.

This inclined Atwoods machine is sketched here:. Newton's Second Law describes the effect of forces on one object. So we must isolate all the forces on mass m 1 and apply it. Then we isolate all the forces on mass m 2 and apply it again. This calls for good free-body diagrams. The hanging mass m1 has only two forces on it; the string pulls up with a force we label T while gravity pulls down with a force we label w:.

We expect the acceleration to be upward and have that drawn beside the free-body diagram. As we might expect by now, this one equation has two unknowns -- tension T and acceleration a -- so we must look elsewhere for additional information. Of course, the place to look is at the other mass.

Carefully construct a free-body diagram showing all the forces acting on mass m 2. To find the net force , we must resolve these vectors into their components. Since the acceleration will be along the direction of the plane, we have chosen that direction as the x-axis. Notice that the angle in this diagram is measured from the y-axis. That means the weight has components of. Make sure you understand the signs and sines! Do not go on until all these components are clear to you!

This provides all the information we need to solve for T and a. As before, we can solve one of these equations for T and substitute that into the other equation and solve for a. From the y-components of the forces on mass m 2 , we can solve for the normal force. This will be important when we take friction into account. Example 7: Two blocks of masses m 1 and m 2 are placed in contact with each other on a smooth, horizontal plane as shown here.

A constant horizontal force F is applied to m 1. What is the acceleration of each mass? In one sense, we can almost solve this example intuitively -- in our head. So its acceleration must be. That's the right answer! But is there nothing more to this question? Simple questions -- the intuitively obvious kind -- make wonderful templates or examples for more difficult problems. Look at all the forces on m 1.

Make a good free-body diagram of the forces acting on m 1. Of course the external force F pushes to the right on the mass m 1. But the other mass -- m 2 -- exerts a force on mass m 1. Observe the following examples of summing two forces:. Observe in the diagram above that a downward vector will provide a partial or full cancellation of an upward vector. And a leftward vector will provide a partial or full cancellation of a rightward vector.

The addition of force vectors can be done in the same manner in order to determine the net force i. Consider the three situations below in which the net force is determined by summing the individual force vectors that are acting upon the objects. As mentioned earlier , a net force i. In a previous unit, several means of representing accelerated motion position-time and velocity-time graphs, ticker tape diagrams, velocity-time data, etc.

Combine your understanding of acceleration and the newly acquired knowledge that a net force causes an acceleration to determine whether or not a net force exists in the following situations.

Click on the button to view the answers. There is a no net force since there is not an acceleration zero slope on a v-t graph means zero acceleration. There is a net force since there is an acceleration the slope on a v-t graph means acceleration. Free-body diagrams for four situations are shown below. For each situation, determine the net force acting upon the object.