[New Book] How Forces Affect Motion Notes Ch 6 Exploration| Simplified!

Want to do great on your science exam? These How Forces Affect Motion Notes Ch 6 are made just for you! We have picked out the most important bits about pushes, pulls, and Newton’s Laws so you can learn them fast.

These notes are great for a quick look before your test, but they work best if you also read your NCERT Science book.

The NCERT book is like a big map that shows you everything in detail, while these notes help you remember the big ideas. Use both together to become a science superstar!

We have also included the main learnings from the many activities of the textbook in “How Forces Affect Motion Notes Ch 6.”

Happy Learning!

The Concept of Force

Force = Push or Pull on an object

Properties of force

● Force has both magnitude (strength) and direction
● It is a vector quantity (like position, displacement, velocity, acceleration)
● If either magnitude, direction, or both change → the effect of force also changes

SI Unit of Force

Examples of Force & Direction

Measuring the magnitude of a force

● Tool used → Spring Balance
● Weight = the gravitational force Earth exerts on an object
● A spring balance measures weight as well as any general force
● How → pull the free end → it measures that pulling force

Balanced and Unbalanced Forces

In real life, more than one force acts on an object simultaneously

Example → Tug of war where both teams pull equally → rope stays still

Net Force Rules

Real-Life Examples

Net force is what actually determines if and how an object moves — not individual forces alone

The Force of Friction: Often Overlooked but Always Present

Do You Need Continuous Force to Keep Moving?

Yes
👉 Force keeps an object moving; friction stops it.

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Friction opposes motion and varies with surface type.

👉 Rough surfaces (like wood) → more friction → object stops
👉 Smooth surfaces (like marble) → less friction → object travels farther

In short,

Different surfaces → different friction → different stopping distances

How to measure friction and compare it on different surfaces.

Use Spring Balance

👉 The spring balance reading = force of friction.
👉 Higher reading → more friction → Object stops.
👉 Lower reading → less friction → Object moves farther.

Newton’s First Law of Motion

The Law (Definition):
An object at rest remains at rest, and an object in motion continues to move with a constant velocity, unless a net force acts upon the object.

Importnat Points

• If net force = 0 → object cannot begin to move or change its velocity
• If net force = 0 → acceleration = 0
• At rest = zero velocity
• Constant velocity = no change in magnitude or direction

When Net Force = 0
Two Cases:

Q: Applied force = Friction force on a moving box. What happens?

A: Both forces are equal & opposite → Net force = 0 → Box continues moving with constant velocity (Newton’s 1st Law)

Newton’s 1st Law covers motion with no net force

Newton’s Second Law of Motion

The Law (Definition)

When a net force acts on an object, the object accelerates in the direction of the net force. The magnitude of acceleration is proportional to the net force and inversely proportional to the mass of the object.

The Formula,

F = ma

Direction of acceleration = direction of net force

Definition of 1 Newton:
Force that produces an acceleration of 1 m s⁻² on an object of mass 1 kg 1 N = 1 kg m s⁻²

Real-Life Example — Cricket Fielder:

● Fielder pulls hands backward while catching a fast ball
● ↑ Time to stop the ball → ↓ acceleration → ↓ force needed
● Result → less injury to the fielder
● Based on → F = ma (less a = less F)

Newton’s 2nd Law is considered a fundamental law of nature

Important:
● Acceleration increases when force increases
a ∝ F
● Acceleration decreases as mass increases
$a∝1/m​$

Newton’s Third Law of Motion

The Law (Definition)
Whenever one object exerts a force on a second object, the second object simultaneously exerts an equal and opposite force on the first object.

Action-Reaction vs Balanced Forces

Real-Life Examples

Chandrayaan-3 — Vikram Lander

• The engine fired in the direction of motion
• Exhaust gases pushed in the opposite direction to the motion
• → Rocket slowed down → achieved safe velocity for soft landing near Moon’s south pole

Newton’s 3rd Law explains why at least two objects are always needed for any force to exist.

Forces Acting on a System of Objects

● Newton’s laws apply to single objects as well as systems of connected objects
● Treating connected objects as a single system simplifies calculations

Internal vs External Forces

In the system approach → only external forces are considered. Internal forces cancel each other out (Newton’s 3rd Law)

Two-Box Problem (Frictionless Surface)

Setup:
Box 1 (m₁) and Box 2 (m₂) are connected by a string, and force F is applied on Box 1

• On Box 1 → F acts (right), T acts (left)
• On Box 2 → T acts (right)

System Approach

• Treat both boxes + string as one single object
• Total mass = m₁ + m₂

Formula:$$a = \frac{F}{m_1 + m_2}$$

• The system accelerates like a single object of mass (m₁ + m₂)

Why Use the System Approach?

• Avoids calculating forces on each object separately
• Gives the same result with much less effort
• Highlights the power of Newton’s Laws for complex systems