Moment Physics

Forces can cause objects to move, but did you know they can also make objects spin? In fact, this spinning is caused by something called a moment. A moment is a force that is exerted on an object, which makes it spin. This is really interesting stuff and it's all part of the world of Moment Physics! So take a moment to learn more about moments and how they work.

Definition of a moment in physics

The word moment has a different meaning in physics than it does in our everyday language. In physics, a moment is the effect that a force has on an object causing it to turn. Objects will rotate around a pivot point if there is a nonzero net moment acting on them. However, if an object is balanced and not rotating, then the net moment acting on it is zero. This happens when the clockwise moment on an object is equal to the anticlockwise moment, canceling each other out. So, in Moment Physics, the word moment refers to the turning effect that a force has on an object.

Formula of moment in physics

Let's say we have an object with a distinct pivot point we apply a force, which we'll call F, on the object. We can draw a line through the point where the force is applied and in the same direction as the force. We then measure the perpendicular distance from the pivot point to that line and call it d. Check out the illustration below for a visual representation of this setup.

The red dot is the pivot point of the brown stick, F is the force on the stick, and d is the distance to the line
The red dot is the pivot point of the brown stick, F is the force on the stick, and d is the distance to the line

 

The size of the moment on an object is determined by the force applied, multiplied by the perpendicular distance from the force to the pivot point. This can be written as M=Fd, where M is the moment, F is the force, and d is the perpendicular distance.

The units for measuring moments are Nm (newton-metres). If a force of 1 N is applied at a perpendicular distance of 1 m from the pivot point, then the moment size would be 1 Nm. It's important to note that moments have the same units as energy (joules), but they are not the same thing. To avoid confusion, moments are denoted in units of Nm to make it clear that we are talking about a moment and not a form of energy.

Sample calculations with moments

To calculate the force required to break the door using the crowbar, we need to consider the moment generated by the force applied to the crowbar.

In this case, the force applied to the crowbar is the force we exert on it, which we'll call F. The perpendicular distance from the pivot point (the point where the crowbar is placed against the door) to the line of force is the length of the crowbar, which we'll call L. The moment generated by the force is then M=FL.

If we assume that the force required to break the door is 4000 N, we can set the moment generated by the force applied to the crowbar equal to this value:

M = FL = 4000 N

We can rearrange this equation to solve for the force required:

F = 4000 N / L

The force required to break the door depends on the length of the crowbar. If the length of the crowbar is 1 meter, then the force required would be:

F = 4000 N / 1 m = 4000 N

If the length of the crowbar is 2 meters, then the force required would be:

F = 4000 N / 2 m = 2000 N

So the longer the crowbar, the less force required to break the door. However, it's important to note that the longer the crowbar, the more difficult it may be to apply force to it, as it requires more leverage and control.

A crowbar (green) is used to break a door (to the right) by using a wall (to the left) to stabilise its pivot (red dot), and where you exert the force F
A crowbar (green) is used to break a door (to the right) by using a wall (to the left) to stabilise its pivot (red dot), and where you exert the force F

I apologize, there was an error in my previous response. The correct calculation is:

M = 4000 N × 0.05 m = 200 Nm

To calculate the force required on the crowbar, we need to divide the moment by the length of the crowbar:

F = M / L

If the length of the crowbar is 1 meter, then the force required would be:

F = 200 Nm / 1 m = 200 N

So the force required to break the door using the crowbar is 200 N, which is a realistic force for a person to exert on an object.

Experiment with moments in physics

If you know your own mass and the distance from the pivot at which you are balanced on a seesaw, you can use the same equation we used to find Bob's position:

mAlicedAlice = mfrienddfriend

If you know Alice's mass and the distance at which she is balanced, then you can solve for your friend massfriend =Alice /

are balanced on a seesaw at a distance of 1.5 meters from the pivot and you weigh 50 kg, and your friend is balanced on the other side at a distance of 2.0 meters from the pivot, then your friend's mass would be:

mfriend = mAlicedAlice / dfriend = 50 kg × 1.5 m / 2.0 m = 37.5 kg

So your friend's mass would be 37.5 kg.

Measurement of moment

By using a known force and varying the distance from the pivot, you were able to determine the moment required to turn the nut. This is a useful technique for determining the torque required for various tasks, such as tightening or loosening bolts or screws. It's important to note that the size of the force required will depend on the specific task and the properties of the materials involved.

A spanner and a nut, with the pivot, string, and the force delivering machine
A spanner and a nut, with the pivot, string, and the force delivering machine

Understanding moments is essential in physics and has many practical applications in daily life, from using tools like spanners to understanding the balance of seesaws and other objects. The ability to calculate and manipulate moments is also important in engineering and other fields that involve designing and building structures and machines.

Moment Physics

What moment means in physics?

A moment in physics is the turning effect on an object caused by a force. Think of applying a force to a steering wheel or a spanner in order to make things spin: these forces exert moments on the objects in question.

How do you calculate moments?

The moment on an object is calculated by multiplying the force on the object by the perpendicular distance of contact point of the force to the object's pivot. It is handy to look at pictures to see what we mean by the term perpendicular distance.

What is difference between moment and momentum?

There is a big difference between moment and momentum. The momentum of an object is a measure of the amount of motion the object possesses, while the moment on an object is a measure of the turning effect being exerted on that object.

What is an example of moment?

An example of a moment in physics is the moment you exert when using a spanner: you exert a force at a certain perpendicular distance to the nut, which is the pivot.

What is the formula and equation for moment?

The equation describing the moment on an object is M=Fd, where F is the force on the object and d is the perpendicular distance of the contact point of the force to the pivot of the object. It is handy to look at pictures to see what we mean by the term perpendicular distance.

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