Lesson Notes By Weeks and Term v4 - JHS 1
FORCE AND MOTION
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FORCE AND MOTION
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Subject: Science
Class: JHS 1
Term: 3rd Term
Week: 4
Grade code: B7.4.4.1.3
Strand code: 4
Sub-strand code: 4
Content standard code: B7.4.4.1
Indicator code: B7.4.4.1.3
Theme: FORCES AND ENERGY
Subtheme: FORCE AND MOTION
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Newton’s First Law of Motion explains why objects keep doing what they are already doing—either staying at rest or moving in a straight line at constant speed—unless a net (unbalanced) force acts on them. This law helps JHS learners understand everyday Ghanaian experiences such as: why passengers jerk forward when a trotro stops suddenly, why a football slows down on a rough field, why seat belts and helmets save lives.
2.1 Force (Quick Reminder) A force is a push or pull that can change an object’s motion (start, stop, speed up, slow down, change direction) or shape. Unit of force: newton (N) Forces can act in different directions. 2.2 Balanced and Unbalanced Forces (Net Force) Balanced forces: forces are equal in size and opposite in direction → net force = 0 N Result: no change in motion Unbalanced forces: forces do not cancel → net force ≠ 0 N Result: motion changes (accelerates, decelerates, turns, starts, stops)
Net force is the overall force after combining all forces.
Example (simple): 10 N to the right and 10 N to the left → net force = 0 N (balanced) 12 N right and 7 N left → net force = 5 N right (unbalanced) 2.3 Newton’s First Law of Motion (Law of Inertia) Statement (standard): > An object remains at rest or continues moving with constant velocity in a straight line unless acted upon by a net external force.
Meaning in simple terms: If nothing “pushes” or “pulls” an object in a new way, it keeps doing what it is doing. At rest stays at rest (until a net force acts). In motion stays in motion (same speed, same direction) until a net force acts. 2.4 Inertia Inertia is the tendency of an object to resist changes in its state of motion. A heavy object (more mass) has more inertia than a light object. That is why it is harder to start pushing a loaded wheelbarrow than an empty one. 2.5 Why Objects Eventually Stop in Real Life (Friction and Air Resistance) Newton’s First Law says motion continues if no net force acts. But in real life, objects slow down because of friction and air resistance, which are forces that oppose motion. Friction: force between surfaces in contact (e.g., ball and ground) Air resistance: force from air opposing motion (e.g., moving bicycle)