# Important Forces: Tension

by Jared Rovny

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00:00 Now that we understand how gravity and the normal force work together to work on a slope problem like the one we just solved, we can introduce one more force which is the tension.

00:09 If I have an object like this one hanging from a bar or a ceiling or something like this from a string or a rope and the gravity is pulling the object downwards and it's not moving, there's certainly a force trying to stop the object from moving and that's the force from the string or the rope.

00:26 This force comes because when we try to stretch a string or a rope or something that doesn't wanna be stretched, it will fight back and have these chemical bonds pulling back inwards.

00:34 So this tension force is existing throughout the rope as we see it here.

00:38 So this tension force is pulling upwards on the object and will react to whatever forces are pulling downwards on the object.

00:45 So the tension force is something that we can find from a problem based on the other forces and the fact that the object is not accelerating, which we'll see below.

00:53 But first something important to point out about the tension force that can be really confusing which is suppose you have a pulley and two masses are suspended from the pulley as I've shown them here.

01:02 Then they're both causing a tension in this rope and the tension is pulling upwards on these two masses.

01:07 One tricky thing is that people often don't realize that the tension in both of these ropes is the same, it's the same tension force.

01:14 So you could, for example, write Newton's second law for the mass on the left, write it again for the mass on the right, and then you could equate the tension forces in both equations that you've just written because the tension force is the same everywhere throughout a given rope or string.

01:27 The second possibly confusing thing is that if we were writing Newton's second law for the pulley, the forces of tension will be acting downwards on the pulley and there wouldn't just be one force of tension even though there's one rope, we would actually say that there's two forces of tension, one on either side acting on the pulley.

The lecture Important Forces: Tension by Jared Rovny is from the course Force.

### Included Quiz Questions

1. Tension applied by a string is the same all along the length of the string.
2. Tension depends on the weight of the mass at each location on the string.
3. Tension must be zero at the fixed end of the string.
4. Tension cannot be applied horizontally.
5. Tension can only act when the string has a pulley to distribute the force.
1. 10N
2. 5N
3. 20N
4. 15N
5. 25N

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