How much work is done when pushing against a brick wall?

Question

So this is one of the questions on my physics assessment and I would like to know how to calculate how much work is done when pushing against a brick wall.

My teacher has told me the calculation is: weight(kg)x10 (this gives me the force)x distance.

But what is the weight of and the distance of? As when you push against a brick wall the wall doesn't move and you can stop yourself from moving.

Please answer as soon as possible, also I'm kind of younger so could you explain clearly(sorry)

Emsee

Answer 1

Emsee,

This is a bit of a trick question.

The equation you have is only correct for calculating the work done against gravity (and then only when you're near earth's surface).

The equation for calculating work is: work (joules) = Force (Newtons) * distance (meters)

Specifically, this says that the work done on an object is equal to the force applied to it multiplied by the distance that force caused it to be moved.

"My teacher has told me the calculation is: weight(kg)x10 (this gives me the force)x distance."

That equation is a specific example of a work calculation: the work done when moving an object up or down against gravity. The 10 represents acceleration due to gravity and is actually 10 meters per second per second (also known as meters per second squared). Always use units.

If the force exerted is not against gravity, it is calculated differently...but don't get started trying to figure out how to do that just yet.

Work=Force*distance

You don't know what the magnitude of your force is, but you know what direction it's in. So how much does the object that the force is applied to move in that direction?

I'll let you figure out the rest since it's a homework problem.

Answer 2

For someone who has never had a physics class, I think it's fairly common to confuse the concepts of energy and force. You're speaking of a force being exerted, then asking what the energetic picture of the situation is. The answer is to simply decouple those two concepts and look at what physics has to say about them. We can formulate the problem several different ways.

• Energy is force times distance. For your problem, no matter how long you push, the wall still goes nowhere, so there is no obvious energy transfer. You're probably wasting energy that goes into body heat, but you do that anyway.

$$ E = F d = F ( 0 )= 0$$

• Power is force times velocity. You also need to know that power is defined to be energy supplied per unit time. You can use this to talk about the power your car's engine is putting into the car's kinetic energy. With this perspective, we discover that no energy is dynamically being transferred at any given point in time.

$$ P = F v = F (0) = 0$$

If you think about it, you are surrounded by a pressure (defined to be force per area) of $14 \text{ pounds force}/{\text{in}^2}$. To drill in the point that force on a static surface doesn't do anything to the energy balance of the world, just consider the incredible forces that the air around you is exerting on you right now. The force is balanced, evidenced by the fact that you're not currently accelerating. When you push on the brick wall, the building distributes your force through its foundation and pushes back in a similar manner.

These infinite invisible forces that permeate your world are difficult to swallow initially, simply because they are invisible.

Answer 3

It would be twice as much work since the "machine" or object does not move or put forth more energy.