12.3 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE
12.3 Newton’s Laws
In grade 10 you learnedabout motion, but did not look at how things start to move. You havealso
learned about forces. Inthis section we will look at the effect of forceson objects and how wecan
make things move.Newton’s First Law ESBEX
Sir Isaac Newton was ascientist who lived in England (1642-1727) whowas interested in the motion
of objects under variousconditions. He suggested that a stationary object will remain stationary unless
a force acts on it and that a moving object willcontinue moving unlessa force slows it down, speeds
it up or changes its direction of motion. From this he formulated what isknown as Newton’s First Law
of Motion:DEFINITION: Newton’s First Law of Motion
An object will remain ina state of rest or continuetravelling at constant velocity, unless
acted upon by an unbalanced (net) force.Let us consider the following situations:An ice skater pushes herself away from the sideof the ice rink and skates across the ice. Shewill
continue to move in astraight line across theice unless something stops her. Objects are also like
that. If we kick a soccer ball across a soccer field, according to Newton’s First Law, the soccer ball
should keep on movingforever! However, in real life this does not happen. Is Newton’s Law wrong?
Not really. Newton’s First Law applies to situations where there aren’t any external forces present. This
means that friction is not present. In the case ofthe ice skater, the friction between the skates and the
ice is very little and shewill continue moving for quite a distance. In the case of the soccer ball, air
resistance (friction between the air and the ball)and friction between thegrass and the ball is present
and this will slow the ball down.