1. Forces: Changes in Motion
Holt Physics
Chapter 4 section 1
Pages

2. What is Force?
Force – the cause of acceleration or the cause of a change in motion.
 a “push” or “pull”

3. Units of Force SI unit of force  Named for Sir Isaac Newton
Newton (N) = 1 kg x m/s2
The amount of force that causes a 1 kg object to accelerate at 1 m/s2

4. What Forces Equal Pounds = force  action by gravity on mass
1 N = .225 lbs
* Force due to gravity = 14,700N

5. Types of Forces 1. Contact Forces - pushes and pulls
resulting from physical contact between 2
objects.
Examples – tug of war, shove in the back, pushing a box

6. Contact Forces

7. Types of Forces
2. Field Force - force existing between objects even with no physical contact.
Examples – Gravity, electrical charges (+ & -)

8. Field Forces

9. Diagrams 1. Force Diagrams
 A diagram of objects involved in a situation
and the forces exerted on objects.
- Sample diagram on page 126 – figure 4-3a
(next slide)

10. Diagrams

11. Diagrams 2. Free body diagram
 A diagram showing only the force acting
on a specific object (of interest)
- Sample diagram on page 126 – figure 4-3b
(next slide)

12. Diagrams

13. Homework: 1. Read p. 129 and then write:
 1 paragraph reaction (at least 5 sentences)
 1 paragraph summary (at least 5 sentences)
2. Page 128 #1-6
3. Read p
4. Read p