# Need help calculating friction and normal force for Measuring Friction Lab

• jillime
In summary, the person is seeking help with calculating friction and normal force for a lab where a wooden block is sliding on a wooden surface with a weight attached to it. They have already found the static and kinetic friction for different weights and surface areas and now need help with the calculations. The normal force can be found by multiplying the total mass of the block and weight by gravity, and the force in the string can be found by multiplying the mass of the hanging object by gravity. The coefficient of static/dynamic friction can be calculated by dividing the force in the string by the normal force, and it should be consistent for the same materials but differ for different materials.
jillime
Need help calculating friction and normal force for "Measuring Friction" Lab

Hey guys, I'm not great at physics and have a lot of work ahead of me so I could use some help.

The lab setup is a wooden block sliding on a wooden surface. There is a weight attached to the block by a string that's hanging from a pulley at the end of the wooden surface.

This guy right here ----> http://imageshack.us/photo/my-images/820/40999170.jpg/ if I'm being unclear.

I have found the weight it takes to start the object moving (static friction) and the weight it takes to move the block at a constant velocity (kinetic friction). I did this a bunch of different times with different weights and surface areas and now I get to do a bunch of calculations.

SO, I could really use a walk-through on simply how to calculate the friction and the normal force, because I have to do it 12 different times.

For example, my first calculation was for the wood on wood block (weighing 128.1g) with a 100g weight on top, it took 81.1 grams to start it moving (static friction). If someone could just give me basic steps to work this out, it would help a lot. (Find friction force and normal force).

This is probably simple but I don't have a physics brain and I'm new to the course. So thanks for the help.

The normal force is just the total mass of your block including whatever you piled on top, times gravity (9.8N/kg).

The force in the string is similarly the mass of the thing hanging over the end of the desk times g.

If you've adjusted the latter to make it just start to move, or move with constant velocity, then you just need to divide the string force by the normal force and that's your coefficient of static/dynamic friction. This is a property of the two materials you are pushing together (assuming their equally smooth/oily/dry/etc). So it should come out the same for any given pair of materials, but be different if you use plastic or metal instead of wood.

## 1. How do I calculate friction?

To calculate friction, you need to first determine the coefficient of friction between the two surfaces in contact. This can be done by dividing the force required to move an object by the weight of the object. Once you have the coefficient of friction, you can multiply it by the normal force to find the frictional force.

## 2. What is the normal force?

The normal force is the force that a surface exerts on an object in contact with it. It is perpendicular to the surface and counteracts the force of gravity on the object. In other words, it is the force that prevents an object from falling through a surface.

## 3. How do I measure the normal force?

The normal force can be measured by using a force sensor or a spring scale. Place the object on a flat surface and then attach the force sensor or spring scale to the object. The reading on the sensor or scale will be the normal force.

## 4. What factors affect friction?

Friction is affected by several factors such as the roughness of the surfaces in contact, the weight of the object, the coefficient of friction, and the presence of lubricants. Other factors like temperature, humidity, and surface area can also have an impact on friction.

## 5. How do I interpret the results of my friction and normal force calculations?

The results of your calculations will give you the magnitude and direction of the frictional force and the normal force. You can compare these values to see how they relate to each other and how they are affected by different variables. You can also use these results to analyze the efficiency of different surfaces and materials in reducing friction.

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