Forces and Newton's Laws of Motion Review

Newton's 1st Law of Motion

An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by an unbalanced force.

Inertia

The tendency of an object to resist changes in its motion (either staying at rest or maintaining constant velocity).

Newton's 2nd Law of Motion

The acceleration of an object depends on the net force acting on the object and the object's mass.

Formula for Newton's 2nd Law

F = m * a, where F is Force (in Newtons, N), m is Mass (in kilograms, kg), and a is Acceleration (in meters per second squared, m/s²).

Newton's 3rd Law of Motion

For every action, there is an equal and opposite reaction.

Mass

The amount of matter in an object. Measured in kilograms (kg). Mass does not change based on location (Earth, Moon, etc.).

Force

A push or pull on an object. Measured in Newtons (N), where 1 Newton = 1 kg • m/s².

Acceleration

The rate at which the velocity of an object changes. Measured in meters per second squared (m/s²). Acceleration occurs when an object speeds up, slows down, or changes direction.

Net Force

The overall force acting on an object when all individual forces are combined.

Calculating Net Force

Net Force is the total force acting on an object after all forces are combined.

Example of Net Force (Same Direction)

Two people push a box in the same direction with 5 N and 10 N. The net force is 5 N + 10 N = 15 N (to the right).

Example of Net Force (Opposite Directions)

Two people push a box in opposite directions with 12 N to the right and 8 N to the left. The net force is 12 N - 8 N = 4 N (to the right).

Newton's 2nd Law Practice Problem 1

A person pulls a sled with a force of 30 N to the right, while friction exerts a force of 10 N to the left. What is the net force on the sled?

Newton's 2nd Law Practice Problem 2

A car has a mass of 1,000 kg and accelerates at 2 m/s². What is the force acting on the car?

Newton's 2nd Law Practice Problem 3

A 5 kg object experiences a force of 20 N. What is the object's acceleration?

Newton's 2nd Law Practice Problem 4

An object accelerates at 3 m/s² when a force of 15 N is applied. What is the object's mass?

Conversion: Kilograms to Pounds

1 kilogram (kg) ≥ 2.2 pounds (lb).

Conversion: Meters to Inches

1 meter (m) ≥ 39.37 inches (in).