Physics Chapter on Force and Gravitation

Force

• Force is a push or pull that can cause an object to accelerate, change its velocity, or deform.
• It's a vector quantity, meaning it has both magnitude (strength) and direction.
• Units of force are Newtons (N).
• Examples of forces include: gravity, friction, normal force, tension, and applied force.
• Net force is the vector sum of all forces acting on an object.
• If the net force on an object is zero, the object will either remain at rest or continue moving at a constant velocity.

Gravitation

• Gravitation is a fundamental force of attraction between any two objects with mass.
• The force of gravity depends on the masses of the objects and the distance between them.
• Newton's Law of Universal Gravitation describes the force of gravity between two objects:
  • The force is directly proportional to the product of the masses (more mass = more force)
  • The force is inversely proportional to the square of the distance between the centers of the masses (greater distance = weaker force).
• The acceleration due to gravity (g) near the surface of a planet or other celestial body depends on its mass and radius.
• Gravitational force is what keeps planets in orbit around the sun and what keeps us grounded on Earth.

Newton's Laws of Motion

• Newton's First Law (Law of Inertia): An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a net force.
  • Inertia is the resistance of an object to changes in its motion. Greater mass means greater inertia.
• Newton's Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
  • Mathematically, F = ma, where F is force, m is mass, and a is acceleration.
  • The direction of acceleration is the same as the direction of the net force.
• Newton's Third Law (Law of Action-Reaction): For every action, there is an equal and opposite reaction.
  • When one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in direction on the first object.
  • Examples include: a rocket propelling itself by expelling hot gas, a person walking, or two magnets repelling each other.

Relationships Between Concepts

• Newton's Law of Universal Gravitation is a specific example of a force.
• Newton's Laws of Motion provide the framework for understanding how forces affect the motion of objects, including objects under the influence of gravity.
• The force of gravity is a central force, meaning it always acts along the line joining the centers of the masses.
• The acceleration due to gravity (on Earth, close to the surface) is approximately 9.8 m/s².