1. Aim: How do we explain Newton’s second law of motion?

2. Do Now:
The greatest increase in the inertia of an object would be produced by increasing
Mass of the object from 1 kg to 2 kg
Net force applied to the object from 1.0 N to 2.0 N
Time that a net force is applied to the object from 1.0 s to 2.0 s
Speed of the object from 1.0 m/s to 2.0 m/s

3. Newton’s Second Law of Motion
Fnet = ma The net force acting on an object is equal to its mass times its acceleration. Force is measured in units called newtons. What is one newton equal to?

4. Net Force
The net force is the vector sum of all the forces acting on an object. Example:
17 N
4 N
What is the net force acting on the box? 13 N to the right

5. Solving Problems with Newton’s 2nd Law
Calculate the force that Clayton Kershaw exerts on a baseball if he accelerates the ball at a rate of 100 m/s2 and the mass of the ball is 0.1 kg.
Fnet=ma
Fnet=0.1kg(100m/s2)=10N
2. A bowling ball of mass 8 kg accelerates from rest to 5 m/s in 2s. What net force is acting on the bowling ball?
a=Δv/Δt=5m/s/2s=2.5m/s2
Fnet=ma=8kg(2.5m/s2)=20N

6. Examples 3 and 4.
3. Calculate the net force acting on a 3 kg box accelerating at 1.2 m/s2. Fnet=ma=3kg(1.2m/s2 )=3.6 N 4. What is the mass of soccer ball if it accelerates at 11 m/s2 when kicked with a 22 N force? Fnet=ma 22N=m(11m/s2) m=2kg

7. Solving Problems with Newton’s 2nd Law
5. Calculate the acceleration of this box. The box has a mass of 2 kg. Fnet=8N to the left Fnet=ma 8N=2kg(a) a=4m/s2
12 N 4N

8. Solving Problems with Newton’s 2nd Law
6) A 2-kg object is moving horizontally with a speed of 4 m/s. How much net force is required to keep the object moving at this speed and in this direction? 0N because the velocity is constant

9. Calculating weight
Weight is the force with which an object is being pulled toward the center of the Earth through gravity. It is equal to an object’s mass multiplied by the acceleration due to gravity Fg = mg Weight = Fg m = mass g= acceleration due to gravity

10. Calculating weight
Calculate the weight of a 60 kg person standing on the surface of the earth.
Calculate the weight of a 0.1 kg pencil.
What is the mass of a 12,000 N elephant?
Fg=mg=60kg(9.8m/s2)=588N
Fg=mg=0.1kg(9.8m/s2)=0.98 N
Fg=mg 12,000N=m (9.8m/s2) m=1225 kg

11. Thought Question-Turn and Talk
On the Earth, the acceleration due to gravity is 9.8 m/s2. On the moon, the acceleration due to gravity is 1.6 m/s2. If you were to travel from the Earth to the moon, what about you would change; your weight or your mass?
Write a sentence explaining your answer.
Your weight would change because the acceleration due to gravity on the moon is different than on earth. Your mass would stay the same.

12. Differences between weight and mass
Weight depends on mass. Weight is affected by acceleration due to gravity while mass is independent of acceleration due to gravity. Mass is a resistance to acceleration.

13. The Normal Force
The normal force is a force which is exerted by an object lying on a surface in a direction perpendicular to the surface.

14. Equilibrium
In physics, equilibrium means that the net force on an object is zero.

15. Regents checkpoint 1
When the sum of all the forces acting on a block is zero, the block
Must be at rest
Must be accelerating
May be slowing down
May be moving at constant speed

16. Regents Checkpoint 2
Which situation represents a person in equilibrium?
A child gaining speed while sliding down a slide
A woman accelerating upward in an elevator
A man standing still on a bathroom scale
A teenager driving around a corner in his car

17. Regents Checkpoint 3
A rock is thrown straight up into the air. At the highest point of the rock’s path, the magnitude of the net force acting on the rock is
Less than the magnitude of the rock’s weight but greater than zero
Greater than the magnitude of the rock’s weight
The same as the magnitude of the rock’s weight
zero

18. Regents Checkpoint 4
Which situation describes an object that has no unbalanced force acting on it?
An apple in free fall
A satellite orbiting Earth
A hockey puck moving at constant velocity across ice
A laboratory cart moving down a frictionless 30 degree incline