CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.3
- A car going at 20 m·s−^1 accelerates uniformly and comes to a stop in a distance of 20 m.
(a) What is its acceleration?
(b) If the car is 1000 kghow much force do thebrakes exert?More practice video solutions or help at http://www.everythingscience.co.za(1.) 00p4 (2.) 00p5 (3.) 00p6 (4.) 00p7 (5.) 00p8 (6.) 00p9
(7.) 00pa (8.) 00pb (9.) 00pc (10.) 00pd (11.) 00pe (12.) 00pf
(13.) 00pg (14.) 00ph (15.) 00pi (16.) 00pj (17.) 00pk (18.) 00pm
(19.) 00pn (20.) 00pp (21.) 00pqNewton’s Third Law of Motion ESBEZ
Newton’s Third Law ofMotion deals with the interaction between pairs of objects. For example, if
you hold a book up against a wall you are exerting a force on the book(to keep it there) and thebook
is exerting a force backat you (to keep you fromfalling through the book). This may sound strange,
but if the book was notpushing back at you, your hand would push through the book! Thesetwo
forces (the force of the hand on the book (F 1 ) and the force of the book on the hand (F 2 )) are called an
action-reaction pair of forces. They have the same magnitude, but actin opposite directions and act
on different objects (theone force is onto the book and the other is ontoyour hand).
There is another action-reaction pair of forces present in this situation. The book is pushing against the
wall (action force) and the wall is pushing backat the book (reaction). The force of the book onthe
wall (F 3 ) and the force of the wall on the book (F 4 ) are shown in the diagram.
wallbook
F 1 : force of hand on book��F 2 : force of book on hand
F 3 : force of book on wall
F 4 : force of wall on bookF 1 F 2
F 3 F 4
Figure 12.6: Newton’s action-reaction pairsDEFINITION: Newton’s Third Law of Motion
If body A exerts a forceon body B, then body Bexerts a force of equal magnitude on
body A, but in the opposite direction.