# Force and Laws of Motion Class 9 Summary

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## 20 Questions

Frictional force

Newton

### When are forces said to be balanced forces?

When they nullify each other and their resultant force is zero

### What does a force consist of?

Both magnitude and direction

### What does a force do to an object it acts upon?

Produces acceleration

Momentum

Force

kg m/s

Inertia

### According to the law of conservation of momentum, what happens to the sum of momenta of two objects before and after collision?

It remains constant

kg m/s

### According to the second law of motion, what is the relationship between the rate of change of momentum and the applied unbalanced force?

Directly proportional

Inertia

### What is the formula for momentum?

$mv$

Remains constant

Newton

Inertia

Force

### When are forces said to be balanced forces?

When their resultant force is zero

Friction

## Study Notes

### Forces and Motion

• A force that always opposes the motion of objects is called friction.
• The SI unit of force is the Newton (N).

### Balanced Forces

• Forces are said to be balanced forces when they result in no net force or acceleration on an object.

### Force and Momentum

• A force consists of a push or pull that causes an object to change its motion.
• A force acting on an object causes it to change its velocity, i.e., accelerate.
• The product of mass and velocity is known as momentum.

### Formulae

• The formula F = ma represents force (F), mass (m), and acceleration (a).
• In the formula F = ma, 'F' represents force.
• The formula for momentum is p = mv, where p is momentum, m is mass, and v is velocity.

### Momentum and Conservation

• The natural tendency of an object to resist a change in its state of rest or of uniform motion is called inertia.
• According to the law of conservation of momentum, the sum of momenta of two objects before and after collision remains the same.
• The SI unit of momentum is the kilogram-meter per second (kg·m/s).
• If the external force on a system is zero, the total momentum of the system remains constant.

### Second Law of Motion

• According to the second law of motion, the rate of change of momentum is proportional to the applied unbalanced force.

Access summary and revision notes for Class 9 Science Chapter 9 on Force and Laws of Motion. These CBSE notes include key points, revision notes, images, and diagrams for comprehensive understanding of the chapter. Ideal for students using NCERT Textbook for Science.

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