# Difference between Tensile Force and Tension

1. Jul 28, 2011

### GreenPrint

What is the difference? If I recall someone telling me there's no sense thing as a force called tension and that the proper term is tensile force but it's all fuzzy at the moment. Does anyone know the difference between the two and can explain?

2. Jul 28, 2011

### middlj

Tension is normally talked of in terms of stress. Tensile force is, well, a force. If you hang a 10N weight on the end of a metal bar, you've applied a 10N tensile force but the stress depends on the cross sectional area of the bar.

3. Jul 28, 2011

### GreenPrint

Ah so like when in the case of the metal bar, if i were to hang the metal bar up onto the ceiling by a string, the force exerted on the string as a opposite in direction and equal in magnitude to the force of gravity acting on the bar would be 10 N of a tensile force or 10 N of a tension force upwards?

4. Jul 28, 2011

### PeterO

I think the difference between tension and tensile force may be similar to the difference between weight and the weight force.

When a string/bar/rod is under tension, it means forces is trying to stretch that string/bar/rod - it is being pulled at each end. The tensile Force is the size of the forces trying to stretch it.

Similarly, when a mass is placed in a gravitational field it will have weight. Here on Earth, the weight force of a 2 kg mass is about 19.6 N

Peter

5. Jul 28, 2011

### GreenPrint

I'm thinking I'm understanding now. So which is more proper to say? I have a feeling the second one but not sure.

There are 10 N of tension acting on the bar.

There are 10 N of a tensile force acting on bar.

When describing the force that's equal in magnitude but opposite in direction of the force of gravity acting on the bar? Also when we assume that the string is a mass less object of a negligible mass aren't we assuming that the string is just some sort of extension of the object that can be considered part of the object but has no mass? So then is it technically improper to draw on a free body diagram the uh... tensile force/force of tension... which ever is more proper??? as being directly upwards out of the object... shouldn't it be at the top of the string that's holding the object in air sense it's considered as some massless entity that's just a extension of the object?

6. Jul 28, 2011

### PeterO

Due to tension in the string, the string pulls up on the bar, and pulls down on the ceiling.
Those two forces are not a Newton's Third law couple however - despite being equal in size and opposite in direction. the couples would be.

The Earth pulls down on the bar (1) , the bar pulls up on the Earth (2)
The bar pulls down on the string (3), the string pulls up on the bar (4)
The string pulls down on the ceiling (5), the ceiling pulls up on the string (6).

In a diagram, not all of those forces are drawn in. You may be considering only the forces acting on the bar [2 & 3] for example.

Forces 1 & 2 are drawn with arrows starting at the centre of mass of the Earth / Bar.

Forces 3 - 6 are drawn with arrows starting at the points of contact between the two bodies.

Peter

7. Jul 29, 2011

### GreenPrint

so would it be more proper to say that there are 10 N of tension acting on the bar exerted by the string or that there's 10 N of tensile force acting on the bar exerted by the string?

8. Jul 29, 2011

### PeterO

I would say "Due to Tension in the string there is a 10N force acting on the bar".