Find Contact Force Between 2 Blocks

• seichan
In summary, the conversation discusses finding the magnitude of the contact force between two blocks on a frictionless table when a horizontal force is applied to one of the blocks. The solution involves using Newton's Second Law (F=ma) and drawing free body diagrams to determine the acceleration and contact force between the blocks. The value of F is given as 4N.
seichan
[SOLVED] Contact Force

Homework Statement

a.Two blocks are in contact on a frictionless table. A horizontal force F Is applied to M2. The force's magnitude is 4 N. [The diagram shows the force pushing on the left side of M2, which has M1 on its right side.]If M1=1.09 kg, M2=3.02 kg, find the magnitude of the contact force between the two blocks.
b. If instead an equal but oppositely directed force -F is applied to M1 rather than M2, find the magnitude of the contact force between the two blocks.

Homework Equations

Alright, right now we're doing Newton's laws of motion, so I'm pretty sure that F=ma is the only relevant equation.

The Attempt at a Solution

We barely brushed upon contact forces and they are not mentioned in our book that I have seen. I checked wikipedia (I know...) and it informed me that when there are two masses and the force is being applied to mass A, then the contact force will be proportional to Mass B. Thus, I went with the assumption that I could do this:

F=M2*A
F/M2=A
A= 4/3.02 m/s^2

I figured I could then apply this to the second block.

F=M1A
F=4.36/4.02 N

I inputted this and it was incorrect. So, I figured that it perhaps was the difference between the two forces. This answer (2.9154) was incorrect as well. I have not even tried part b yet, knowing that the method involved is the same. I went to study group on Tuesday and the group leader claimed that it would just be 4 N. As you can probably guess, that is incorrect as well. Any help you can give would be very appreciated.

Last edited:
What is the value of F? You can't put a number on the value of the contact force if the value of F is not given. It would have to be determined as a function F, using free body diagrams.

I'm sorry- the value of F is 4 N. I forgot to type this in. I will add it right away.

OK, F=4N. That's the applied force. You are now looking for the contact force between the 2 blocks. Although the Wikepedia solution (that you noted) is correct, it is not a good starting point for a beginner. You've got to start with the basics, Newton's 2nd law, F_net = Ma. I'd first look as the system of the 2 blocks as a whole, and apply Newton 2 to that system (the blocks must move together). What do you get for the acceleration? Then since each mass alone must accelerate at that same value, draw a free body diagram of the 2nd block (that is , isolate it from the other block), and note the unknown contact force acting on it, and use Newton 2 again to solve for it. Do the same for Part B.

Thank you very much.

What is contact force?

Contact force is the physical force that is exerted between two objects when they come into direct contact with each other.

How do you calculate contact force?

Contact force can be calculated by multiplying the coefficient of friction between the two objects by the normal force, which is the force perpendicular to the surface of contact.

What factors affect the magnitude of contact force?

The magnitude of contact force is affected by the weight, surface area, and coefficient of friction of the two objects in contact.

What is the difference between static and kinetic friction?

Static friction is the force that prevents two objects from sliding past each other when there is no relative motion between them, while kinetic friction is the force that opposes the motion of two objects that are already in motion.

How does the angle of incline affect the contact force between two blocks?

The angle of incline can affect the magnitude of contact force between two blocks, as it changes the weight and normal force acting on the objects. As the angle increases, the normal force decreases, resulting in a decrease in contact force between the blocks.

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