Introduction

In this science experiment, we will learn the relationship between the weight of a body and the force required just to move it.

Friction

You must have studied friction in your previous classes, although below are the main points about friction for a quick revision to understand the experiment quickly.
Here, N= Normal force
F= Contact force
f= force of friction

Some Important points:

1. Friction is the force exerted between two bodies kept in contact. Whatever we do in our daily lives involves friction—for example, walking on a road, writing your notes, riding a bicycle or pulling/pushing an almirah.
f = μN
Where μ is the coefficient of friction
N is the normal

2. Friction obeys Newton’s third law.
3. According to Newton’s third law, every action has an equal and opposite reaction, i.e. if a body A exerts a force F on another body B, then B will exert a force -F on A.
4. This force can operate between a pair of solids, between a couple of liquids and between a solid or liquid.

Types of Friction

1. Static Friction

This force of friction acts between two bodies kept in contact but do not slip on each other. For example, when someone is trying to push a heavy truck. The maximum force applied to a car does not make it move due to its heaviness, and this maximum force is called limiting friction. The coefficient of this friction is denoted with μs.

2. Kinetic Friction

This force of friction acts between two different moving bodies kept in contact. For example, riding a bicycle. The coefficient of this friction is denoted with μk.

Laws of Friction

1. The direction of kinetic friction acting on a body is opposite to the body in motion with respect to the body applying the force of friction.

2. If the bodies slip over each other, the force of friction between them will be
fk  =  μk.N

3. If the bodies do not slip over each other, the force of friction between them will be
fs  ≤  μs.N

Note:  Friction not only opposes the motion but also causes the motion.

Aim of The Experiment

To set up a relationship between the weight of a wooden block lying on a horizontal table and the maximum force required to move it using a spring balance.

Requirements

1. Rectangular wooden block with a hook,
2. A spring balance,
3. Five wooden pieces of equal mass,
4. A fine thread,
5. A weight box.

Theory

Whenever a force is applied on an object kept over a surface, and it doesn’t move, this means friction is acting between these two surfaces, and this friction is called static friction. The maximum force needed to move this object is called limiting friction. When a body starts moving, the static friction between them will change into kinetic friction.

Procedure

Step 1: Clean the table on which you are going to perform this experiment.
Step 2: Place the wooden block on it.
Step 3: Take the spring balance. Note its least count and zero error.
Step 4: Tie one end of the thread with the hook of the wooden block and the other end of it to spring through a thread.
Step 5: Place this whole thing in such a way that one end of the table holds a wooden block, and the other end holds spring balance.

Step 6: Now, slowly pull the spring balance until the wooden block starts moving.
Step 7: Note the reading showing on spring balance; it shows the force applied on the wooden block to make it move.
Step 8: Now, put the additional weight on the wooden block and repeat steps 7 and 8.
Step 9: Do step 9 for all the masses.

Observation

Least count of spring balance =………….

Zero error in spring balance = …………

Weight of the wooden block =…………..

Calculations

1. Plot a graph between normal reaction along the X-axis and reading of spring balance along the Y-axis.

2. You will receive a straight line graph.

Result

It is observed that when the weight on wooden pieces increases, the normal force also increases. Thus the graph shows that the maximum force required to move the rectangular block is directly proportional to the mass of the rectangular piece.

Precautions

1. Thread should be strong enough to pull the wooden block.
2. Table should be dry and clean.
3. Before use, the spring balance should be of zero error.
4. Note the reading on spring balance only when the wooden block starts to move.
5. The mass of the wooden block should not be so large.

Conclusion

In this article, we have learnt the relationship between the weight of a body and the force required just to move it.

VIVA Questions With Answers

Q.1 What is the SI unit of friction?

Ans. Newton

Q.2 Why do wooden blocks not move on the first go?

Ans. Due to friction and the minimum applied force.

Q.3 Why do wooden blocks start dating after a specific amount of force is applied to them?

Ans. When the applied force crosses the limiting friction, wooden pieces start moving.

Q.4 Friction follows which law of Newton?

Ans. Newton’s third law.

Q.5 Why is it suggested to clean tables before experimenting?

Ans. Because dust increases the friction.

NCERT Lab Manual Questions

Question 1: In which direction does the force of friction act on the block?

Answer: The force of friction acts in the opposite direction to the direction of the block’s motion.

Question 2: Why thread is pulled horizontally?

Answer: In order to find the friction force, we have to slide the body horizontally on the surface; therefore, it is pulled horizontally.

Question 3: How does oil or grease affect the limiting friction of objects?

Answer: Oil or grease makes the surface smooth which reduces the friction force between objects.

Question 4: How is the concept of limiting friction used to measure a force?

Answer: A body does not move until the force crosses the limiting friction line. Limiting friction can be measured when an object starts moving suddenly after applying a certain amount of force.

Cisco Ramon

Cisco Ramon is an American software engineer who has experience in several popular and commercially successful programming languages and development tools. He has been writing content since last 5 years. He is a Senior Manager at Rude Labs Pvt. Ltd.