2. 2.1 Combining Forces force contact force noncontact force net force
unbalanced forces
balanced forces
Newton’s first law of motion

3. 2.1 Combining Forces
Force
When more than one force acts on an object, the combined effect is caused by the sum of all applied forces.
A push or a pull on an object is a force.

4. Contact and Noncontact Forces
2.1 Combining Forces
Contact and Noncontact Forces
A contact force is exerted only when two objects are touching.
A noncontact force is exerted when two objects are not touching.
Magnets exert a noncontact force on each other.

5. Force is a Vector Vectors have magnitude and direction.
2.1 Combining Forces
Force is a Vector
Vectors have magnitude and direction.
Force has a direction and a magnitude.
Force is measured in Newtons.

6. 2.1 Combining Forces
Combining Forces
When more than one force acts on an object, the forces combine.
The combination of all the forces acting on an object is called the net force.

7. Combining Forces in the Same Direction
Forces are vectors and require a reference direction.
When forces in the same direction combine, the net force is in the same direction and the size of the force is the sum of the forces.

8. Combining Forces in the Same Direction (cont.)
If two people push the dresser to the right, the forces are added together.

9. Combining Forces in Opposite Directions
When forces in opposite directions combine, the net force is in the direction of the larger force.
The size of the net force is the difference between the two forces.

10. Combining Forces in Opposite Directions (cont.)
Two people exerting a force in opposite directions show how vectors combine to create net force.

11. Unbalanced and Balanced Forces
2.1 Combining Forces
Unbalanced and Balanced Forces
If the net force on an object is not zero, it is an unbalanced force.
If the net force on an object does equal zero, it is a balanced force.

12. 2.1 Combining Forces
Balanced Forces

13. Balanced Forces and Motion
2.1 Combining Forces
Balanced Forces and Motion
If two people push with the same force, the dresser does not move.
The forces have the same magnitude.
The forces are in opposite directions.
The net force on the dresser is zero and the forces are balanced.
The motion of the dresser does not change.

14. Unbalanced Forces and Motion
2.1 Combining Forces
Unbalanced Forces and Motion
Unbalanced forces change motion.
If two people push with different force, the dresser moves.
The forces have a different magnitude and are in opposite directions.
The net force on the dresser is not zero and the forces are unbalanced.
The dresser moves in the direction of the larger force.

15. Newton’s First Law of Motion
2.1 Combining Forces
Newton’s First Law of Motion
If the net force on an object is zero, the velocity of the object does not change.
If the net force is zero and the object is at rest, it remains at rest.
If the net force is zero and the object is moving, it continues to move in a straight line with constant speed.
Newton’s Laws of Motion

16. Inertia and Mass Mass is the amount of matter in an object.
2.1 Combining Forces
Inertia and Mass
Mass is the amount of matter in an object.
The more mass an object has, the more inertia it has and the harder it is to change its motion.
A bicycle is easier to push than a car because it has less mass.

17. 2.1 Combining Forces
Which of the following changes occur when an unbalanced force acts on an object?
A motion
B mass
C inertia
D weight
Lesson 1 Review

18. 2.1 Combining Forces
What is the net force acting on a door if one person pushes to the right with a force of 2000 N and a second person pushes with a force of 1500 N to the right?
A 3500 N to the right
B 3500 N to the left
C 500 N to the left
D 500 N to the right
Lesson 1 Review

19. B You turn at constant speed. C You coast to slow down.
2.1 Combining Forces
You are riding a bike. In which of the following situations are the forces acting on the bike balanced?
A You pedal to speed up.
B You turn at constant speed.
C You coast to slow down.
D You pedal at constant speed.
Lesson 1 Review

20. Balanced & Unbalanced Forces
Balanced Skateboard Forces
Draw the skateboard and the vectors in each direction to cause balanced forces.
Unbalanced Skateboard Forces
Draw the skateboard and the vectors in each direction to cause unbalanced forces.
Balanced Frisbee Forces
Draw the frisbee and the vectors in each direction to cause balanced forces.
Unbalanced Frisbee Forces
Draw the frisbee and the vectors in each direction to cause unbalanced forces.