Lesson 4: Forces and Newton's Laws
Understanding Forces and Newton's Laws
Forces are interactions that cause objects to accelerate. Newton's laws of motion describe the relationship between the motion of an object and the forces acting on it.
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.
Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. (F = ma)
Newton's Third Law states that for every action, there is an equal and opposite reaction.
Example Problems
Example problem:
A car is at a stop light. When the light turns green, the car reaches a velocity of 10 m/s north in 5 seconds. What was the acceleration?
Solution:
Acceleration = Change in velocity / Time
= (10 m/s - 0 m/s) / 5 s
= 2 m/s²
Another example:
A person has a mass of 55 kg. How much does this person weigh on Earth?
Solution:
Weight = Mass * Gravitational acceleration
= 55 kg * 9.8 m/s²
= 539 N
Example problem:
A 10 kg box is at rest on a table. Calculate the normal force exerted by the table.
Solution:
Normal force = Weight of the box
= Mass * Gravitational acceleration
= 10 kg * 9.8 m/s²
= 98 N