1. Introduction to Force and Motion:
    • Earlier, motion was described in terms of position, velocity, and acceleration.
    • The cause of motion was a mystery until scientists like Galileo and Newton developed a new approach.
    • In everyday life, effort is needed to move a stationary object or stop a moving object. This effort is called force.
  2. What is Force?:
    • Force can change the motion of an object, like its speed or direction, and can also change its shape.
    • Force is not something we can directly see or touch but we can observe its effects, such as pushing, hitting, or pulling an object.
  3. Balanced and Unbalanced Forces:
    • Balanced forces: When two forces of equal magnitude act in opposite directions on an object, the object does not move.
    • Unbalanced forces: If one force is greater than the other, the object moves in the direction of the larger force. This happens when forces are unbalanced, like when pushing a box on a rough floor, where friction opposes the motion.
  4. Examples of Force in Action:
    • A box on a rough floor doesn’t move unless the applied force exceeds the frictional force.
    • When riding a bicycle, stopping pedaling causes the bike to slow down due to friction. To keep moving, continuous pedaling (force) is required.
  5. Newton’s First Law of Motion:
    • Newton’s First Law: An object stays at rest or keeps moving at a constant velocity unless acted upon by an external force.
    • This tendency of objects to resist changes in their motion is called inertia.
    • Inertia is why we feel thrown forward when a car suddenly stops, or fall backward when a bus accelerates suddenly.
  6. Inertia in Everyday Life:
    • Inertia explains various experiences, like feeling thrown forward in a car when it stops or being pushed backward when the bus starts moving.
    • A carom coin activity demonstrates inertia: when a fast-moving coin hits the bottom coin in a stack, the rest of the coins stay at rest due to inertia.
  7. Inertia and Mass:
    • Heavier objects have more inertia, meaning they resist changes in their motion more than lighter objects.
    • This explains why it is easier to push an empty box than a box full of books.
  8. Mass and Inertia Relationship:
    • Mass is a measure of inertia. Objects with more mass (like a train) have more inertia than objects with less mass (like a cart).
    • This means that a larger force is needed to change the motion of heavier objects.
  9. Summary of Inertia:
    • All objects resist changes to their motion, whether they are at rest or in motion.
    • The mass of an object is directly related to its inertia. More mass = more inertia, and harder it is to change its state of motion.

Additional Concepts to Understand:

  • Force: A push or pull that causes an object to move or change its state of motion.
  • Friction: The force that resists motion between two surfaces in contact. It often works opposite to the direction of motion.
  • Inertia: The resistance of an object to change its state of rest or motion.
  • Mass: The amount of matter in an object, which determines its inertia.
  • Unbalanced Force: A force that causes a change in the motion of an object.

1. Change in Motion and Force

  • When an object’s velocity changes, it experiences acceleration. The amount of acceleration depends on the force applied.
  • Everyday examples show that the impact of objects (like a cricket ball) depends on their mass and speed. A heavier or faster object causes more impact.

2. Momentum

  • Momentum is a property of an object that combines its mass and velocity:
    Momentum (p) = mass (m) × velocity (v)
  • Momentum has both size and direction. The direction of momentum is the same as the object’s velocity.
  • The unit of momentum is kilogram meter per second (kg m/s).
  • A force changes an object’s momentum, which means a force can affect how fast an object moves (acceleration).

3. Second Law of Motion

  • Newton’s Second Law: The rate of change of momentum of an object is proportional to the force applied. This means that the more force applied, the more the momentum of an object will change.
  • The force applied on an object depends on both its mass and the time the force is applied. A bigger force or more time gives a greater change in momentum.

4. Mathematical Formulation of Second Law

  • The second law can be written as: Force (F) = mass (m) × acceleration (a) where acceleration is the change in velocity over time.
  • For example, if a car accelerates, the force needed depends on its mass and how fast its velocity changes.

5. Force and Time

  • For an object to reach a certain speed, a force must be applied for a certain time. The longer the time, the less force is needed to achieve the same change in velocity.

6. Real-World Examples

  • When a fielder catches a fast-moving ball, pulling his hands backward reduces the force on his palms because it increases the time to stop the ball.
  • In high-jump events, athletes land on soft beds or sand to slow down their fall over a longer time, reducing the impact force.
  • In karate, a quick, forceful hit (with a fast-moving fist) can break a solid object because of the high velocity.

7. First Law of Motion

  • Newton’s First Law states that an object at rest stays at rest, and an object in motion stays in motion unless acted upon by an unbalanced force.
  • This is known as inertia. The greater the mass, the greater the inertia, meaning it resists changes to its motion.

8. Third Law of Motion

  • Newton’s Third Law: For every action, there is an equal and opposite reaction. This means when one object pushes on another, the second object pushes back with the same force but in the opposite direction.
  • Example: When you push the ground while walking, the ground pushes you forward with equal force, causing you to move.

9. Examples of Action and Reaction

  • A gun firing causes a bullet to move forward, but the gun experiences a backward “recoil.” This is the action and reaction in opposite directions.
  • Similarly, a sailor jumping off a boat causes the boat to move backward.

10. SI Units

  • The SI unit of force is the Newton (N), defined as the force that causes a 1 kg mass to accelerate at 1 m/s².
  • Momentum’s unit is kg m/s.

THESE ALL ARE THE NOTES OF CHAPTER 8 SCIENCE. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊