# Calculating Contact Forces between Blocks

• sailsinthesun
You can then use Newton's third law to find the contact force between m1 and m2.In summary, the problem involves three blocks in contact on a frictionless surface, with a horizontal force being applied to one block. The masses and force are given, and the magnitude of the contact forces between m1 and m2 and m2 and m3 need to be calculated. To solve this, the acceleration of the system must first be calculated, which is found to be (22/9)m/s^2. Then, using F=ma and drawing a free body diagram for m2, the magnitude of the contact force between m1 and m2 can be found. Finally,
sailsinthesun

## Homework Statement

Three blocks are in contact with each other on a frictionless, horizontal surface, as in Figure P5.54. A horizontal force F is applied to m1. Take m1 = 2.00 kg, m2 = 3.00 kg, m3 = 4.00 kg, and F = 22.0 N.

(c)What is the magnitude of the contact force between m1 and m2?

(d)What is the magnitude of the contact force between m2 and m3?

http://img129.imageshack.us/img129/3048/p556ow4.gif

f=ma

## The Attempt at a Solution

I'm clueless, as we haven't be taught anything about contact forces. Any help?

Last edited by a moderator:
First you need to calculate the acceleration of the system because acceleration of all masses are the same. Next you can draw an FBD and use F=ma to solve c) and d)

AFG34 said:
First you need to calculate the acceleration of the system because acceleration of all masses are the same. Next you can draw an FBD and use F=ma to solve c) and d)

I calculated acceleration of the system to be (22/9)m/s^2.

Would it be F=(m2-m1)a?

for C) draw an FBD for M2

## 1. How do you calculate contact forces between blocks?

To calculate contact forces between blocks, you need to first determine the normal force acting on each block. This can be done by using the weight of the block and the surface it is resting on. Next, you need to consider any external forces acting on the blocks, such as friction or applied forces. Finally, you can use Newton's third law of motion to calculate the contact force between the two blocks, which is equal in magnitude but opposite in direction for each block.

## 2. What is the difference between static and kinetic friction?

Static friction is the force that resists the motion between two objects that are not moving relative to each other. It is always equal in magnitude to the applied force until the object starts moving. Kinetic friction, on the other hand, is the force that resists the motion between two objects that are already in motion relative to each other. It is typically less than static friction and is dependent on the materials and surfaces in contact.

## 3. How does the surface area of a block affect contact forces?

The surface area of a block can affect contact forces in two ways. First, a larger surface area means there is more area in contact between the two blocks, which can increase the normal force and therefore the contact force. Second, a larger surface area can also increase the amount of friction acting between the blocks, which can also affect the contact force. However, the exact relationship between surface area and contact forces depends on the specific materials and surfaces involved.

## 4. Can you calculate contact forces between blocks if they are on an incline?

Yes, you can still calculate contact forces between blocks on an incline. The key is to resolve the forces into components parallel and perpendicular to the incline. The perpendicular component will determine the normal force, while the parallel component will determine the friction force. You can then use these components to calculate the contact force between the blocks using Newton's third law.

## 5. How do contact forces between blocks affect the motion of an object?

The contact forces between blocks can affect the motion of an object by either slowing it down or speeding it up. Friction forces, for example, can act in the opposite direction of motion and cause an object to slow down. On the other hand, applied forces can accelerate an object in the direction of the force. The magnitude and direction of the contact forces will ultimately determine the resulting motion of the object.

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