1. Forces and the Laws of Motion
Chapter 4

2. Chapter4 Section 1: Changes in Motion Section 2: Newton’s First Law
Section 3: Newton’s Second and Third Law
Section4: Everyday Forces

3. Friday January 8th
Describe how force affects the motion of an object. Interpret and construct free body diagrams.

4. Forces

5. Force
A force is an action exerted on an object which may change the object’s state of rest or motion.
Forces can cause accelerations.
The SI unit of force is the newton, N.
Forces can act through contact or at a distance.
In other words….
Change the velocity of an object…
Acceleration = change in velocity
change in time

6. Contact vs Field forces
Contact forces: result from physical contact between two objects (applied force, normal force….)
Field Forces: do not involve physical contact (gravity, electrostatic repulsion/attraction)

7. Force Diagrams
The effect of a force depends on both magnitude and direction. Thus, force is a vector quantity.
Diagrams that show force vectors as arrows are called force diagrams.
Force diagrams that show only the forces acting on a single object are called free-body diagrams.

8. Force Diagrams, continued
Section 1 Changes in Motion
Chapter 4
Force Diagrams, continued
Force Diagram
Free-Body Diagram
In a force diagram, vector arrows represent all the forces acting in a situation.
A free-body diagram shows only the forces acting on the object of interest—in this case, the car.

9. Practice
Draw a free-body diagram of the toy these puppies are playing with.

10. Homework
Copy the example on page 121. (copy all the bold text into your notes.)
Complete practice questions 1-2 on page 122
And section 1 formative assessment questions 2, 3, 4, 5