1. Chapter 4: Forces in One Dimension

2. Launch Lab on pg. 87
Which string broke in step 2?
Which string broke in step 3?

3. Force and Motion Force: a push or a pull on an object
Forces can cause an object to:
Speed up, slow down, change directions
Direction in which the force is exerted also plays a role

4. Force and motion
F is a symbol that for a vector and represents the size and direction of a force
F just represents magnitude

5. Considering how force affects motion
Consider the object “called system” and everything around the object that exerts forces on it is called the external world

6. Contact force vs. field force
Contact force examples: touch something to apply a force
Field force examples: gravitational force from the earth acts on objects without touching them, also magnets
There needs to be an agent causing a force on a system (example: your hand “agent” causes a force on the book “system”

7. Free-Body Diagrams The object is represented with a “dot”
Represent each force with an arrow that points in the direction that the force is applied
The length of the arrow should proportional to the size of the force
Always draw the force arrows pointing away from the particle even when the force is a push
Label each force
Choose a direction that represent (+)  this is usually the direction with the greatest force because it makes the problem easier to solve and reduces negative values

8. Practice problems

9. Force and Acceleration
Would an object continue to accelerate when there was no longer a force applied?
Think about a spaceship in outer space…does it have velocity? Is there still a force acting on it? Could it accelerate?

10. Force and Acceleration
The relationship between force and acceleration is a linear relationship where the greater the force is, the greater the resulting acceleration.
Talk about the cart pulled by a stretched rubber band example, if you pull more carts with the same rubber band…acceleration decreases therefore… the slope in an acceleration vs. force graph is dependant on mass

11. F = ma
a = F/m … tells you that a force applied to an object causes that object to experience a change in motion, the force causes the object to accelerate.
It also tells you that for the same object if you double the force, the acceleration doubles

12. What is the unit for force?
If F=ma (Newton’s 2nd law)… then one unit could be: kg·m/s2
1 kg·m/s2 = 1 Newton (N)

13. Think about different objects falling
Acceleration as we learned is the same due to gravity
Therefore different objects have different masses, and therefore require different amounts of forces.

14. Combining forces
Net force: the vector sum of all the forces on an object

15. Equal and opposite direction forces
Net force = __________N
Draw a picture below

16. Equal or unequal forces same direction
Net force =
Draw a picture below

17. Unequal forces opposite directions
Net force =
Draw a picture below

18. Equal or Unequal forces perpendicular
Net force =
Draw a picture below

19. Newton’s First Law
“an object that is at rest will remain at rest, and an object that is moving will continue to move in a straight line with constant speed, if and only if the net force acting on the object is zero”

20. Newton’s First Law Inertia- the tendency of an object to resist change
Equilibrium- if the net force on an object is zero, then the object is in equilibrium (if it is at rest or if it is moving at a constant velocity)
As long as the object is not experiencing a change in speed or direction is at equilibrium

21. Table 4-2
Force
Symbol
Definition
Direction

22. Table 4-2
Force
Symbol
Definition
Direction

23. Section Review pg. 95
9-12, 14.

24. Section Review pg. 95
9-12, 14.