The Impulse-Momentum Change Theorem – Mechanical Engineering

# The Impulse-Momentum Change Theorem

Momentum

The sports announcer says, “Going into the all-star break, the Chicago White Sox have themomentum.” The headlines declare “Chicago Bulls Gaining Momentum.” The coach pumps up his team at half-time, saying “You have the momentum; the critical need is that you use thatmomentum and bury them in this third quarter.”

Momentum is a commonly used term in sports. A team that has the momentum is onthe move and is going to take some effort to stop. A team that has a lot of momentum is really on the move and is going to behard to stop. Momentum is a physics term; it refers to the quantity of motion that an object has. A sports team that is on the move has the momentum. If an object is in motion (on the move) then it has momentum.

Momentum can be defined as “mass in motion.” All objects have mass; so if an object is moving, then it has momentum – it has its mass in motion. The amount of momentum that an object has is dependent upon two variables: how muchstuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object.

Momentum = mass • velocity

In physics, the symbol for the quantity momentum is the lower case p. Thus, the above equation can be rewritten as

p = m • v

where m is the mass and v is the velocity. The equation illustrates that momentum is directly proportional to an object’s mass and directly proportional to the object’s velocity.

The units for momentum would be mass units times velocity units. The standard metric unit of momentum is the kg•m/s. While the kg•m/s is the standard metric unit of momentum, there are a variety of other units that are acceptable (though not conventional) units of momentum. Examples include kg•mi/hr, kg•km/hr, and g•cm/s. In each of these examples, a mass unit is multiplied by a velocity unit to provide a momentum unit. This is consistent with the equation for momentum.

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