# Help Torque

1. Sep 15, 2004

### jazjackson12

Help!! Torque

undefinedundefined Hello, please help me answer this question using definitions, principles, and reasoning: How does the torque that a doorstop exert on a door (as the door crashes into it), coming to a stop suddenly, compare to the torque you exert on a door to start it opening? Is the doorstop torque larger, doorstop torque smaller, or are our torques the same?

2. Sep 15, 2004

### Tide

That depends on where you place the doorstop and on how fast you open or close the door! :-)

3. Sep 16, 2004

### HallsofIvy

Staff Emeritus
What forces are you applying to the door and what distance from the hinges? Those are the two things that determine torque.

4. Sep 17, 2004

### ShawnD

It's been like half a semester since I did torque so excuse any errors

IIRC, one of the formulas dealing with torque was

$$M = I_c \alpha$$

M is basically torque, alpha is acceleration, and Ic you can just ignore. Quicker angular acceleration means more torque.

5. Sep 17, 2004

### BobG

Actually, it's more a conceptual problem and than actually having to solve the equation. ShawnD gives you the equation for determining torque, except alpha is angular acceleration to be more precise.

Angular acceleration is the rate that the angular velocity is increasing or decreasing. If your torque is constant, the longer you apply it, the greater your change in angular velocity. The shorter you apply it, the less your angular velocity changes.

In this problem, the change in angular velocity is constant. The amount of time it takes to change your angular velocity is not. Therefore, the amount of torque applied must be different, as well.