1. Chapter 6 One last thing…

2. Newton's 3 rd Law states that…

3. The force that object A puts on B is the same as object B puts on A (just in opposite directions) We can interpret this to mean that F A on B = -F B on A

4. What are the two things that make up force??

5. So can’t we substitute ma for F? Won’t this work? m A x a A = -m B x a B

6. What variables are we given? Practice problem: A 65 kg boy and a 45 kg girl use an elastic rope while engaged in a tug-of-war on an icy, frictionless surface. If the acceleration of the girl towards the boy is 3 m/s 2, find the acceleration of the boy towards the girl.

7. I have masses and accelerations for two different objects… Mass of boy = 65 kg Mass of girl = 45 kg Acc of girl = 3 m/s 2 Acc of boy = ?

8. Since we don’t have force, we will use the mass and acceleration.. Yes!! Use Newton’s 3 rd Law F A on B = -F B on A

9. 65 x a = 45 x 3 65a = 135 a = 2.1 m/s 2

10. We are done. Quiz on Friday.