Physics PHY101: Force and Newton's Laws

Force and Newton's Laws

• The study of force and its effect on motion is called dynamics.
• Before Newton's time, people believed that the natural state of everything is to come to rest, and that a force is needed to keep something moving.
• Newton said that the natural state of everything is to maintain its motion, and that a force is needed to change its motion.

Newton's First Law of Motion

• The first law states that everything remains at rest or moves with a constant speed unless an external force acts on it.
• This means that a body moving will keep moving on its own without the application of an external force.
• The concept of frame of reference is important, as different observers may measure different distances and velocities.

Force and Acceleration

• Force is a vector that has a magnitude and direction, and it causes acceleration.
• The direction of the force is the same as the direction of the acceleration.
• Force is measured in units of Newtons (N), and it can be calculated using the equation F = ma, where m is the mass of the object and a is its acceleration.
• The equation F = ma can also be used to define mass, as m = F/a.

Types of Forces

• Contact forces occur when two bodies come into contact with each other, such as when we push a box or when air exerts pressure on a moving car.
• Examples of contact forces include friction, air resistance, and tension.
• Non-contact forces, such as gravity, can also act on an object.

Action and Reaction

• When two bodies interact, they exert equal and opposite forces on each other.
• Examples of action-reaction pairs include a person pushing a wall and the wall pushing the person back, or a person pulling a sledge and the sledge pulling the person back.
• Action-reaction forces do not cancel each other out, because they act on different objects.

Newton's Second Law of Motion

• The second law states that the total external force acting on a body is equal to the product of its mass and acceleration.
• Mathematically, this can be written as F = ma, where F is the total external force, m is the mass, and a is the acceleration.
• This law can be used to calculate the acceleration of an object given the force acting on it and its mass.

This quiz covers forces and Newton's laws, building on previous concepts of kinematics, including displacement, velocity, and acceleration in one, two, and three dimensions.