Why it gets easier to push open a door, the further you are from the hinge?
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With a constant applied force (pushing open a door), the torque on a lever (bird’s eye view of the door) is proportional to the distance from the fulcrum (the hinge)
the term for it is called mechanical advantage. you are trying to rotate the door on the hinge, and the torque to create that rotation is equal to the force applied times the distance from the hinge.
Simple word: **Leverage**. Base word: **Lever**.
Remember your simple machines from school? The first was **Lever** (then Wheel and axle, Pulley, Inclined plane, Wedge and Screw).
A door is a lever, with the fulcrum being the hinge.
As the lever rotates around the hinge, points farther from this pivot move faster than points closer to the hinge. Therefore, a force applied to a point farther from the pivot must be less than the force located at a point closer in, because power is the product of force and velocity.
Familiar with torque? Torque is measured in ft/lbs (foot pounds). Basically, a measure of a weight at a fixed distance from the pivot.
**20 ft/lbs** is a force equivalent of a 20-pound weight hanging on the end of a wrench 1 foot long. But, if your wrench is TWO feet long (doubled) you only require TEN pounds hanging on the end to equal 20 ft/lbs.
Thus, the longer the wrench, the less weight (effort) it takes to get the same result.
Note: upon rereading, maybe that my memories of work are incorrect and that I may have mixed it with energy. To ease comprehension without learning wrong premices about physics, assume that “work” is more a concept, rather than the scientific term.
Let’s try this approach:
To open a door, or even, to do anything, you need to perform some actions in order to complete a task. A task will require a certain amount of **work**.
The course of action to open a door will require you to expend energy to push the door. In other terms, it requires a certain amount of work to open it. This amount is generally fixed, I mean your door doesn’t randomly become harder or easier to be opened each and every time you do, does it?
Now, to successfully open it, you need to meet the amount of work required to do so. Assuming the door has no locks, you can do it in a lot of way:
– you can traditionally push it by the knob, which will require some force along some distance to be done;
– you can lean against it, the gravitational pull of Earth will generate much more work than needed to open the door, thus slamming the door against the wall and you slamming on the floor flat;
– you can kick it, your body will also produce much more work than needed to push that door open, which will slam hard on the wall.
But, why opening it by pushing near the hinge is harder? Remember, the amount of work to open the door is constant. We’ve stated that, opening the door along the knob requires a fixed amount of force along a fixed distance. The distance is big, since you push the far end of the door all the way to opened, and the force is of some quantity. If you push the near side of the door open, you drastically reduce the amount of distance you have to go, since the radius is now a few inches. But the amount of work needed is still the same to open the door, so to compensate a **shorter** distance, you need a **bigger** force.
Easy example: 20 * 5 = 100. But if suddenly 20 becomes halved, 10, then 5 needs to be doubled, so it becomes 10. 10 * 10 = 100.
Work = force x distance
Lets say w needs to be 100 to open the door
100=fd
If d is 10, f is 10
If d is 20, f is 5
If d is 50, f is 2
So as d increases, the force required decreases
Torque (circular force) = Force x Length of lever arm. Longer arm (further from hinge) multiplies your force.
Head down to your local park and check out the see-saw, the beam is the lever and the pivot is the falcrum.
On a door the hinge is the falcrum, and door is the lever, but the opposite side of the see-saw is 0 length.
But same princibles apply close to falcrum little movement, less fun, away from falcrum, more movement less force required.
Leverage.
Have you ever tried to ride a seesaw with your friend but sitting closer to the middle? Its a lot harder to make it go up and down as opposed to if you two were sitting at the edges.
A lever requires more energy in order to move the closer you get to the fulcrum. THe hinges are the fulcrum.
The short version of any sort of “mechanical advantage” explanation is that if you divide the work over twice as much distance then you only have to push half as hard.
When you push something on hinge, you push along the arc of a circle. If you’re twice as far from the hinge you have to push half as hard twice as far.
The answer is torque. You are able to apply a lot more torque due to the distance from the fulcrum.
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