Module 3—Effects of Force on Velocity
Explore
Newton’s laws of motion are physical laws that describe the relationship between the force acting on a body and the motion of the body. All three laws were first published in Latin in Newton’s book titled Philosophiae Naturalis Principia Mathematica (1687). Together, his three laws form the backbone of classical mechanics, which is the branch of physics concerned with explaining the behaviour of physical bodies as they are subjected to forces. You will explore Newton’s first and second laws in the following activities.
Newton’s First Law: Law of Inertia
Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum,
nisi quatenus a viribus impressis cogitur statum illum mutar.
The modern translation of the first law is as follows:
A body continues in its state of rest or of motion in a straight line with a constant speed unless an external, unbalanced force acts on it.
inertia: a property of matter that causes matter to resist changes in speed or direction
This law is also referred to as the law of inertia. Inertia refers to an object’s ability to resist changes in its velocity. All objects resist changes in their motion, which is why an unbalanced force must be applied in order to change an object’s velocity. Inertia is related to the object’s mass: a heavier object will resist changes in its velocity to a greater extent than a similar object of less mass. Therefore, a more massive object has a greater amount of inertia.
Newton’s first law implies the following:
- An object that is at rest will stay at rest until an unbalanced force acts upon it, giving it motion.
- An object that is in motion will not change velocity until an unbalanced force acts upon it.
The first point seems obvious. The second point, however, is not as easily understood since an object rarely maintains a constant velocity for an extended period. The world is far too full of unbalanced forces to observe constant velocity in the real sense.
Read
Read pages 137 to 139 of your textbook to see examples of Newton’s first law and inertia.
Self-Check
SC 1. What do you call the tendency of objects to resist any change in their velocity?
SC 2. Why do objects in motion usually come to rest despite their inertia?
SC 1. The tendency of objects to resist any change in their velocity is called inertia.
SC 2. Objects in motion usually come to rest despite their inertia because the unbalanced forces of friction and air resistance continually decrease the speed of the objects. In other words, friction and air resistance give objects a negative acceleration.
Try This
TR 1. Complete “3-3 QuickLab: Challenges with Inertia” on page 138 of your textbook; then answer question 1.
TR 2. Go to page 142 of your textbook and answer question 4 of “3.2 Check and Reflect.”
Newton’s first law says, in essence, that the velocity of an object remains constant (either at zero or a steady non-zero value) unless acted on by an outside unbalanced force. What happens if it is acted on by an outside unbalanced force? Complete the following lab to find out.