🧧 Forces
1. A force is experienced as a push, pull or lift.
2. A force cannot be seen, but its effects can be felt.
1. A force can:
- (a) move a stationary object,
- (b) stop a moving object,
- (c) speed up or slow down a moving object,
- (d) change the direction of a moving object, and
- (e) change the shape (and size) of an object.
1. When two forces acting on an object are equal in size and act in opposite directions, they balance each other out. These are called balanced forces.
2. A stationary object will remain stationary if there are no forces acting on it, or if the forces acting on it balance each other out.
Balanced forces (8 N = 8 N) — the object does not move; its state of motion stays the same.
Unbalanced forces (12 N > 8 N) — the effects of a force can be observed; the object's motion changes in the direction of the larger force.
1. Forces are grouped into two types:
- (a) contact forces — act only when objects are in physical contact: frictional force and elastic spring force, and
- (b) non-contact forces — act without direct contact between objects: magnetic force and gravitational force.
1. Magnetic force is the force of attraction (pulling) and repulsion (pushing) exerted by a magnet.
2. It is a non-contact force that can act on an object from a distance and can pass through thin, non-magnetic objects.
1. Gravitational force is the force of attraction (pull) between objects that have mass.
2. It is a non-contact force that can act on an object from a distance.
Weight is a measure of the amount of gravitational force acting on an object. It is measured in {A("Newtons (N)")}. It is not the same as mass.
Mass is the amount of matter in an object, independent of gravity. It is measured in {A("kg / g")}.
3. The gravitational force acting on an object on Earth is the same regardless of its height above the ground.
4. The amount of gravitational force acting on an object depends on its mass: the greater the mass of an object, the greater the gravitational force acting on it.
When a ball is released from Position A and moves downwards to Position B, the amount of gravitational force acting on the ball remains constant.
This occurs because gravitational force acting on an object on Earth is the same regardless of its height above the ground — so the graph is a horizontal straight line.
1. Frictional force opposes motion between two surfaces in contact.
2. It acts opposite to movement.
- Importance of friction — provides grip (e.g., walking without slipping, gripping tools).
- Downside of friction — causes wear and tear (e.g., soles of shoes, machine parts).
3. Factors that affect the amount of frictional force:
- (a) mass of the object — greater mass → more friction,
- (b) roughness of surface — rougher surface → more friction, and
- (c) presence of lubricants / rollers / wheels — reduces friction.
The amount of frictional force does not depend on the surface area in contact.
1. Air resistance opposes the motion of objects through air.
2. Water resistance opposes the motion of objects through water.
3. The greater the surface area → the greater the resistance → the slower the movement.
4. Streamlined shapes reduce resistance, helping objects move faster.
Two sheets of paper were dropped from the same height. Sheet Q (larger surface area) fell slower due to greater air resistance, while sheet P (smaller surface area) fell faster.
1. Elastic spring force is exerted when a spring is stretched (pulling) or compressed (pushing).
- The extension / compression of a spring increases with greater applied force.
- More springs used → greater total spring force.
- If stretched beyond the elastic limit, the spring is permanently deformed.
The extension graph always starts at 0 (extension of the spring is 0 cm when no weights are hung).
P is less stiff — greater extension for the same load. Q is stiffer — less extension for the same load.