Everything Science Grade 11

12.3 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

See video: VPkjr at http://www.everythingscience.co.za

Newton’s action-reaction pairs can be found everywhere in life wheretwo objects interact with one
another. The following worked examples will illustrate this:

Example 14: Newton III - seat belt

QUESTION

Dineo is seated in the passenger seat of a car with the seat belt on. The car suddenly stops

and he moves forwards until the seat belt stops him. Draw a labelled force diagram identifying

two action-reaction pairs in this situation.

SOLUTION

Step 1 : Draw a force diagram

Start by drawing the picture. You will be usingarrows to indicate the forces so

make your picture largeenough so that detailedlabels can also be added. The

picture needs to be accurate, but not artistic! Use stickmen if you have to.

Step 2 : Label the diagram

Take one pair at a time and label them carefully.If there is not enough space on

the drawing, then use akey on the side.

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F 1 : The force of Dineo on the seat belt

F 2 F 1

F 2 : The force of the seat belt on Dineo

F 3 : The force of Dineo on the seat (downwards)

F 4

F 3

F 4 : The force of the seat onDineo (upwards)