http://www.ck12.org Chapter 7. Momentum
7.1 Momentum
Objectives
The student will:
- Know how momentum is defined
- Be able to solve problems using momentum
Vocabulary
- momentum:An object’s tendency to stay in motion, calculated as the product of its mass and velocity. Mo-
mentum has both magnitude and direction, so is a vector quantity.
Introduction
Heavier objects are harder to stop. The same is true of faster-moving objects. These observations are described well
in Newton’s Laws. An alternate way of analyzing the same tendency, though, is the property ofmomentum. Within
a given reference frame, an object’s momentum is defined as the product of mass and velocity, and is represented by
the letterp, making the formula~p=m~v. The arrows indicate that both momentum~pand velocity~vhave direction,
and thus are vector quantities.
Most people understand that being hit by a 100-kg person running at 3.0 m/s is less desirable than being hit by a
50-kg person running at 3.0 m/s. Intuitively, we recognize that being hit by a small mass is preferable to being hit
by a large mass when they are moving with the same velocity.
FIGURE 7.2
100-kg moving 3.0 m/s.