1. Dynamics 2 – Newton’s Second Law Mr. Jean
Physics 11
Dynamics 2 – Newton’s Second Law
Mr. Jean

2. The plan: Video clip of the day Newton’s Second Law Mass vs. Weight
Newton’s Third Law
Questions

3. Newton’s Second Law: “to move an object with mass you need a force.”
the acceleration of an object is directly proportional to the net force on it and inversely proportional to its mass.
Force = (mass)(acceleration)
F = m a

4. International Units (SI)
Quantity
Symbol
SI Unit
Force
Mass
Acceleration F m a
N (Newtons)
Kg (Kilograms)
m/s2 (metres per second squared)

5. F = m a

6. A net force acting on an object causes it to accelerate.
The larger the mass of an object, the smaller the acceleration. Thus a massive object has more inertia than a less massive object.

7. Unit of force - a force that causes a mass of one kg to accelerate at a rate of one meter per second squared is one newton (N).
F = ma = (1.00kg)(1.00m/s2 ) = 1.00N
1N = 1kgm/s2

8. Common misconception:
WEIGHT DOES NOT EQUAL MASS!

9. Weight:
An objects weight is Fg is the product of its mass m, and the acceleration due to gravity, g.
Fg = mg
Fg = force of gravity in newtons (N)
m = mass in kilograms (kg)
g = acceleration due to gravity (m/s2)

10. Weight calculation: You have an object which has a mass of 40 kg.
What is the objects weight?

11. Newton’s Third Law:
“For every action there is an equal and opposite reaction.”
when one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude but opposite in direction.

12. Example Questions:
What net force is required to accelerate a kg race car at 3.00 m/s2 on a frictionless surface?

14. Forces are vectors:
Forces are vectors. To understand the effects of forces in two directions, we assign signs. If we sum up the forces acting on an object, we can find the net force acting on an object.

15. P.133 Gravity table: Here is the weight of 1000g.
1) What is the weight this object on Earth?
2) ... on the moon?
3) ... on Jupiter?

16. To do for tomorrow:
P. 137
Questions 1-4

18. Chapter #4 Page 137 Questions 1 to 4
Weight Questions
Chapter #4
Page 137
Questions 1 to 4

19. P.137 – Weight Questions