2. Combining Forces - The Nature of Force
The combination of all forces acting on an object is called the net force.

3. Unbalanced Forces - The Nature of Force
Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.

4. Balanced Forces - The Nature of Force
Balanced forces acting on an object do not change the object’s motion.

5. Asking Questions - The Nature of Force
Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.
Question
Answer
What is a force?
A force is a push or pull.
What happens when forces combine?
Forces combine to produce a net force.

6. Gravity - Friction and Gravity
Two factors affect the gravitational attraction between objects: mass and distance.

7. Gravity - Friction and Gravity
The force of gravity on a person or object at the surface of a planet is known as weight.

8. - Friction and Gravity

9. Free Fall - Friction and Gravity
Use the graph to answer the following questions.

10. Free Fall - Friction and Gravity Interpreting Graphs:
What variable is on the horizontal axis? The vertical axis?
Time is on the horizontal axis, and speed is on the vertical axis.

11. Free Fall - Friction and Gravity Calculating:
Calculate the slope of the graph. What does the slope tell you about the object’s motion?
The slope is 9.8. The speed increases by 9.8 m/s each second.

12. Air Resistance - Friction and Gravity
Falling objects with a greater surface area experience more air resistance.

13. Comparing and Contrasting
- Friction and Gravity
Comparing and Contrasting
As you read, compare and contrast friction and gravity by completing a table like the one below.
Friction
Gravity
Pulls objects toward one another
Effect on motion
Opposes motion
Types of surfaces involved, how hard the surfaces push together
Depends on
Mass and distance
Measured in
Newtons
Newtons

14. Calculating Force F = ma F = 55 kg x 2 m/s2 = 110 N
- Newton’s First and Second Laws
Calculating Force
A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration.
Read and Understand
What information have you been given?
Mass of the water-skier (m) = 55 kg
Acceleration of the water-skier (a) = 2.0 m/s2
F = ma
F = 55 kg x 2 m/s2 = 110 N

15. Calculating Force Practice Problem - Newton’s First and Second Laws
What is the net force on a 1,000-kg object accelerating at 3 m/s2?
3,000 N (1,000 kg X 3 m/s2)

16. Newton’s First Law
If no forces are exerted on an object, the object continues in its original state of motion
Newton’s Second Law
The acceleration of an object is proportional to the force acting on it and inversely proportional to the mass of the object
F = ma What if a=0 ?
Newton’s Third Law
If two objects interact they exert equal forces on each other in opposite directions

17. Newton’s First and Second Laws
Newton’s First Law of Motion
Inertia
Inertia Depends on Mass
The Second Law of Motion
Changes in Force and Mass

18. Calculating Momentum - Newton’s Third Law
Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s?
Read and Understand
What information have you been given?
Mass of smaller sledgehammer = 3.0 kg
Velocity of smaller sledgehammer = 1.5 m/s
Mass of larger sledgehammer = 4.0 kg
Velocity of larger sledgehammer = 0.9 m/s

19. Momentum = Mass X Velocity Perform the calculation.
- Newton’s Third Law
Calculating Momentum
Momentum = Mass X Velocity
Perform the calculation.
Smaller sledgehammer = 3.0 kg X 1.5 m/s = 4.5 kg•m/s
Larger sledgehammer = 4.0 kg X 0.9 m/s = 3.6 kg•m/s

20. Calculating Momentum Practice Problem - Newton’s Third Law
A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is kg and the mass of the baseball is 0.14 kg. Which has the greater momentum?
Golf ball: kg X 16 m/s = 0.72 kg•m/s
Baseball: 0.14 kg X 7 m/s = 0.98 kg•m/s
The baseball has greater momentum.

21. Conservation of Momentum-
- Newton’s Third Law
Conservation of Momentum
In the absence of friction, momentum is conserved when two train cars collide.

22. What Is a Satellite? - Rockets and Satellites
A projectile follows a curved path because the horizontal and vertical motions combine.

23. What Is a Satellite? - Rockets and Satellites
The faster a projectile is thrown, the father it travels before it hits the ground. A projectile with enough velocity moves in a circular orbit.

24. What Is a Satellite? - Rockets and Satellites
Depending on their uses, artificial satellites orbit at different heights.

25. Graphic Organizer Type of Friction Occurs When Example Static Sliding
Friction between an unmoving book and desk
An object is not moving
Static
Two solid surfaces slide over each other
Sliding
Rubber pads on a bicycle’s brakes
Rolling
An object rolls across a surface
Ball bearings in skateboard wheels
A solid object moves through a fluid
Fluid
Air resistance