Newton's Laws of Motion

Newton's First Law of Motion

• Statement: An object at rest will remain at rest unless acted on by an unbalanced force. Similarly, an object in motion will continue in motion unless acted on by a net force.
• Explanation:
  • Object at Rest: If a box is on a surface and forces are balanced (e.g., weight force and normal force), it remains at rest.
  • Object in Motion: On a rough surface, like a carpet, a rolling ball quickly stops because of friction—a net force. On a smooth surface, like ice, it travels far due to less friction.
  • Frictionless Environment Example: In outer space, little to no friction, allowing planets like Earth to orbit without slowing down.
• Key Points:
  • Net force equals zero for objects at rest or moving with constant velocity.
  • Acceleration occurs if the net force is not zero.

Newton's Second Law of Motion

• Statement: The net force is equal to the mass times the acceleration (F = ma).
• Proportionality:
  • Net force is proportional to both mass and acceleration.
  • Increase mass, constant force: acceleration decreases.
  • Increase acceleration, constant force: net force increases.
• Examples:
  • Doubling mass, constant acceleration: force doubles.
  • Relationship with momentum: Force equals the rate of change of momentum.
• Impulse-Momentum Theorem: Impulse (force times time) equals change in momentum.

Newton's Third Law of Motion

• Statement: For every action, there is an equal and opposite reaction (FA = -FB).
• Examples:
  • Throwing a basketball: Force exerted on ball results in opposite recoil.
  • Person on a boat throwing a ball: Throwing direction causes boat to move opposite.
  • Astronaut throwing an object in space: Direction thrown determines direction of movement due to reaction force.

Example Problems

1. Constant Velocity (Car):

   • Net force is zero; acceleration is zero.
   • Frictional force example: Applied force balances friction for net zero.

2. Acceleration (Box on Frictionless Surface):

   • Applying force on 10 kg box: Acceleration calculated using F = ma.
   • Calculate final speed and time to reach speed using acceleration.

3. Net Force with Friction (Box):

   • Applied vs. Frictional Force: Net force and acceleration calculation.
   • Determine distance traveled using kinematic equations.

4. Acceleration and Force (Moving Object):

   • Use of velocity change over time to find acceleration.
   • Calculation of net force and applied force considering friction.

5. Astronaut in Space:

   • Throwing a package: Calculate force exerted and acceleration.
   • Example of Newton's third law with equal and opposite forces.

6. Skaters' Reaction:

   • Interaction of forces between skaters: Calculation of acceleration and forces based on different masses.

Key Concepts

• Constant Velocity: No net force means constant velocity and zero acceleration.
• Net Force and Acceleration: Directly related; changes in one affect the other.
• Action-Reaction: Forces occur in pairs, equal in magnitude but opposite in direction.

Additional Resources

• Check out supplemental videos and materials on physics, chemistry, and math at video-tutor.net for further learning.