Betsy has a Ph.D. in biomedical engineering from the University of Memphis, M.S. from the University of Virginia, and B.S. from Mississippi State University. She has over 10 years of experience developing STEM curriculum and teaching physics, engineering, and biology.
What Are Forces?
Amil is trying to move a box of books across the floor. How can he move it? He's got to push on it! When he pushes on it, what he's really doing is exerting a force on the box. A force is a push or pull that changes the motion of an object. Forces can make objects start or stop moving, speed up or slow down objects that are already moving, or make objects change direction.
There are two essential components of a force, known as magnitude and direction. The magnitude of a force is the total amount of force exerted. If Amil pushes on his box of books a little harder, then the magnitude of the force he is exerting will go up. The direction, or which way, that the force is exerted is equally important. If Amil wants to move his box across the room, it won't help much to push on the top of the box, no matter what the magnitude of his force is! He needs to push in the direction he wants it to start moving!
An error occurred trying to load this video.
Try refreshing the page, or contact customer support.
You must cCreate an account to continue watching
Register to view this lesson
As a member, you'll also get unlimited access to over 84,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.
Get unlimited access to over 84,000 lessons.Try it now
Already registered? Log in here for accessBack
Drawing Force Arrows
Force arrows are used to represent both the magnitude and direction of forces. The length of the arrow corresponds to the magnitude of the force, with longer arrows indicating forces with larger magnitudes. The direction of the arrow corresponds to the actual direction that the force is being exerted. Force arrows are used by scientists and engineers to predict the motion of an object based on the forces that are applied to it.
Let's go back to Amil and his box for a moment. To represent the force that he is exerting on the box, we can draw the box and then show the force using a force arrow, like this:
How would our force arrow change if he pushed the box with twice as much force? Because the magnitude of the force is doubled, the length of the force arrow should also be doubled.
Now, what if he didn't push directly to the right, but instead his arms made a 30-degree angle with the ground? In that case, the direction of the force arrow needs to change to show the direction in which the force is applied.
In many physics problems, it's important to identify all the forces that act on an object accurately. These forces are then represented using force arrows on a picture called a free-body diagram. To create a free-body diagram of an object, you need first to identify all of the forces that act on an object.
Let's try to identify all the forces that act on Amil's box of books. You already know that there is a force exerted by Amil on the books, but this is not the only force that acts on the box of books. The Earth's gravity is responsible for a force that pulls down on the box and keeps it from floating away.
In addition, the floor pushes up on the box, and there is some friction between the box and the floor, which results in a friction force that is directed in the opposite direction to the way the box is moving.
You can show all these forces on a free-body diagram of the box and then use it to predict the motion of the box.
These force arrows tell you something about how the box will move. In this case, because the force of Amil's push is bigger than the force of friction, the box will speed up as it moves to the right.
What if he suddenly quit pushing it? It's pretty clear that the box will slow down and stop if that happens, but a free-body diagram can help to explain why this happens.
Now, you can see that there is a net force to the left instead of to the right. This means that if the box was initially moving to the left when he stopped pushing it, it will slow down and eventually stop.
All right, let's take a moment to review what we've learned. A force is a push or pull that changes the motion of an object. Forces can make objects start or stop moving, cause objects that are already moving to speed up or slow down, or make objects change direction.
As we also learned, force arrows are used to represent both the magnitude and direction of forces. The magnitude of a force is the total amount of force exerted, and it corresponds to the length of the force arrow. The direction, or which way, that the force is exerted is equally important, and the force arrow should always be drawn in the same direction that the force is acting.
To unlock this lesson you must be a Study.com Member.
Create your account
Register to view this lesson
Unlock Your Education
See for yourself why 30 million people use Study.com
Become a Study.com member and start learning now.Become a Member
Already a member? Log InBack
Using Force Arrows in Physics Diagrams
Related Study Materials
Explore our library of over 84,000 lessons
- College Courses
- High School Courses
- Other Courses
- Create a Goal
- Create custom courses
- Get your questions answered