Newton’s 2nd Law of Motion

Newton’s Back! He revolutionizes science again with his second law of motion to describe the relationship between force, mass, and acceleration.

In what direction does the acceleration occur? UNBALANCED FORCES What happens to an object when there are unbalanced forces acting upon it? Acceleration. In what direction does the acceleration occur? The direction of the resulting net force. west east Net force = 3 N east

NEWTON’S SECOND LAW OF MOTION: States that the unbalanced force acting on an object equals the object’s mass times its acceleration. Force equals mass times acceleration. Force (F) = mass (m) X acceleration (a) F = ma or (m = F/a) or (a = F/m) Force is measured in newtons (N). Mass is measured in kilograms (kg) Acceleration is measured in (m/s2) 1 N = 1 kg X 1 m/s2 F m a

FORCE/ACCELERATION RELATIONSHIP If mass stays constant… As force increases then acceleration increases m = F/a Direct Relationship ( or )  Same Mass  Force  Acceleration  Force  Acceleration 

FORCE/MASS RELATIONSHIP If acceleration stays constant… As mass increases then force increases a = F/m Direct Relationship ( or ) Same Acceleration Mass  Force  Mass  Force 

MASS/ACCELERATION RELATIONSHIP If force stays constant… As mass decreases then acceleration increases F = ma Inverse Relationship ( or ) Same Force Mass  Acceleration  Mass  Acceleration 

F = ma Problem #1 What is the force of a 25 kg ball accelerated at 9.8 m/s2 downward? F m a

F = ma Problem #2 A 63 kg skater pushes off from a wall with a force of 300 N. What is the skater’s acceleration traveling north? F m a

F = ma Problem #3 If a rock has an acceleration of 40 m/s2 and hits with a force of 285 N, what is its mass? F m a

Conceptual Questions F m a If you kick a bowling ball and a volleyball with the same force, which will accelerate faster? Why? Use Newton’s second law to explain why batters can’t hit a softball as far as a baseball. F m a

Exit Ticket: #9-12

9. What is the force of a 10 kg ball accelerated at 12 m/s2 west? 120 N west 1200 N c. 120 kg d. 1200 kg west

10. What is the SI base unit for mass? a. gram b. pound c. Kilogram d. milligram

11. If force stays constant, then as mass decreases acceleration _______________. a. increases b. decreases c. stays the same d. Not enough info given

12. If mass stays constant, as force increases acceleration ______________. a. Increases b. stays the same c. Decreases d. Not enough info given