1. 11.5 Forces

2. Gravity
Gravity A force that acts downward toward the center of the earth. Falling Objects Gravity pulls down, air resistance pushes up Terminal Velocity A constant velocity when the gravitational force and the air resistance force is equal

3. Terminal Velocity

4. Aristotle, Galileo and Newton
Aristotle (Greek philosopher) Started the study of force, much of his theories were wrong. Galileo (Italian Scientist) Concluded that gravity produces constant acceleration, He also concluded that moving objects that were not subjected to a force, would continue to move forever Newton (Scientist who studied in England)

5. Newton’s 1st Law
Newton’s 1st Law of Motion Also know as the Law of Inertia An object in motion wants to stay in motion and an object at rest will stay at rest unless acted on by an outside force. Inertia The tendency of an object to resist a change in motion

7. Inertia – Bumper Cars

8. Inertia – Bicycles

10. Inertia – Bicycles

11. Newton’s 2nd Law
Newton’s Second Law Also known as the Law of Acceleration The object Force is equal to its mass times the acceleration. Formula: Force = m x a F = force (Newton’s or N) m = mass (kg) a = acceleration (m/s2)

12. Newton’s 2nd Law
The more mass, the greater the force is needed to accelerate an object
The less mass, the smaller the force is needed to accelerate an object

13. Newton’s 3rd Law Newton’s Third Law
Also known as the Law of Interaction
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
For every action there is an opposite and equal reaction.

15. Weight vs. Mass
Weight The force of gravity acting on an object Weight = mass x acceleration due to gravity Weight = m (kg) x 9.8 m/s2 Mass is measured by the inertia of an object

17. Math Examples Example #1
A certain net force acting on a 5 kg mass produces an acceleration of 2 m/s2. Calculate the force. (Hint: Use Newton’s 2nd law of Motion)

18. Math Examples Example #2
What is the weight of a 50 kg girl if the acceleration due to gravity is 9.8 m/s2?
Example #3
What is the weight of the same girl if the acceleration due to gravity was 1.57 m/s2?