CHAPTER-8 FORCE AND PRESSURE
NOTES
1. Force- The push (impulse) or pull (attraction) exerted on an object is called force. Thus, we can say that the motion imparted to objects occurs due to the application of force.
- A force is exerted between two objects due to the interaction between them.
- Forces applied in the same direction on an object combine with each other.
- If two forces act on an object in opposite directions, the total (net) force acting on it is equal to the difference between the two forces. Thus, one force can be greater, smaller, or equal to the other. The intensity of a force is typically measured by its magnitude.
- The speed of an object can be changed by applying force to it. If the force is applied in the direction of motion, the speed of the object increases. If the force is applied in the opposite direction to the motion, the speed of the object decreases.
- Any change in an object's speed, its direction of motion, or both is expressed as a change in its state of motion. Thus, force can bring about a change in the state of motion of an object.
- Applying force can change the shape of an object.
2. Effects of Force-
- Force can bring an object from a state of rest into motion.
- It can change the speed of a moving object.
- It can change the direction of a moving object.
- It can change the shape of an object.
3. Contact Force-
1. Muscular Force- When we push an object or lift a bucket of water, the force is exerted by the muscles of our body. The force applied as a result of the action of our muscles is called muscular force.
- Muscular force can only be applied when the muscles are in contact with an object; hence, it is called a contact force.
2. Friction- The force that causes a change in the state of motion of objects is called frictional force. Frictional force acts on all moving objects and always acts in the direction opposite to the motion.
4. Non-contact Force-
1. Magnetic Force- A magnet can exert force on another magnet without being in contact with it. The force applied by a magnet is an example of a non-contact force.
2. Static Electric Force- The force exerted by a charged object on another charged or uncharged object is called static electric force. This force acts even when the objects are not in contact. Therefore, static electric force is another example of a non-contact force.
3. Gravitational Force- Objects fall towards the Earth because it attracts them. This force is called gravitational force or simply gravity. It is an attractive force.
Pressure - The force applied per unit area on a surface is called pressure.
Pressure = Force / Area on which it is applied.
5. Atmospheric Pressure- There is air all around us, and this layer of air is called the atmosphere. Atmospheric air extends several kilometers above the Earth's surface. The pressure exerted by this air is called atmospheric pressure.
- The force applied per unit area is called pressure.
Pressure exerted by liquids and gases - Gases exert pressure on the walls of the container in which they are placed.
