Page 1 - CLASS VII Lesson Notes Forces and Energy

SAI International School

CAMBRIDGE LOWER SECONDARY

Class- VII
Subject – Physics

CH- Forces and Energy

LESSON NOTES

SUBTOPIC: 3.1 FORCES AND MOTION

Key Words
force, balanced, unbalanced, friction, contact force, weight, air resistance, direction, speed up, slow down,
change direction, opposite, analogy

Understanding Forces
• Force is a push or a pull. It can change the speed, direction, or shape of an object.
• The unit of force is the newton (N).
• Arrows are used in force diagrams to show the direction and size of a force. A longer arrow means a
larger force.

Balanced Forces
• When forces acting on an object are equal in size and opposite in direction, they are balanced.
• Balanced forces do not cause a change in motion. The object stays still or keeps moving at the same
speed in the same direction.
• It may change in shape.

Example:
A rock on the ground:
• Weight pulls it down.
• The ground pushes it up with an equal force (contact force).
• The rock does not move → forces are balanced.

Unbalanced Forces
• Unbalanced forces happen when:
o One force is bigger than the other.
o Forces act in different directions that do not cancel each other out.
• Unbalanced forces cause movement — the object will:
o Speed up
o Slow down
o Change direction
o May change shape
Examples:
1. A rock being pushed by a truck:
o Push from the truck > friction
o The rock starts moving → unbalanced force.

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