Momentum Chapter 3

What is momentum? Read the following quotes. Think about the way we use the word momentum.

The sports announcer says, "Going into the all-star break, the Chicago White Sox have the momentum.“ 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 that momentum and bury them in this third quarter."

Momentum is a commonly used term in sports. A team that has the momentum is on the 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 be hard 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 = mass velocity

Recall What is mass? – Units? What is velocity? – Units?

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.

Recall What does it mean to be directly proportional?

What are the units of momentum? The standard metric unit of momentum is the kgm/s. – Most common Examples include kgmi/hr, kgkm/hr, and gcm/s

Momentum is a vector quantity. a vector quantity is a quantity that is fully described by both magnitude and direction. a vector quantity

What is the momentum of a 5-kg bowling ball moving westward at 2m/s? Looking for: momentum (p) Given:mass (m) = 5 kg Velocity (v)= 2m/s Relationship: p=mv Solution:p= (5kg)(2m/s) p= 10 kg m/s westward

To fully describe the momentum of a 5-kg bowling ball moving westward at 2 m/s, you must include information about both the magnitude and the direction of the bowling ball.

It is not enough to say that the ball has 10 kgm/s of momentum; the momentum of the ball is not fully described until information about its direction is given. The direction of the momentum vector is the same as the direction of the velocity of the ball.

It is not enough to say that the ball has 10 kgm/s of momentum; the momentum of the ball is not fully described until information about its direction is given. The direction of the momentum vector is the same as the direction of the velocity of the ball.

Momentum needs to be described using direction. What does it mean to have positive or negative direction? A common choice is to make positive momentum to the right and negative momentum to the left.

Try the following problems in this format. Looking for: Given: Relationship: Solution: 1. Determine the momentum of a... a. 60-kg halfback moving eastward at 9 m/s. b kg car moving northward at 20 m/s. c. 40-kg freshman moving southward at 2 m/s.

a. Looking for: momentum (p) Given: mass (m)=60kg Velocity (v)= 9m/s EAST Relationship: p = m*v Solution: p= 60 kg*9 m/s p = 540 kgm/s, east

b. Looking for: momentum (p) Given: mass (m)=1000kg Velocity (v)= 20m/s NORTH Relationship: p = m*v Solution: p = m*v = 1000 kg*20 m/s p = kgm/s, north

c. Looking for: momentum (p) Given: mass (m)=40kg Velocity (v)= 2m/s SOUTH Relationship: p = m*v Solution p = m*v = 40 kg*2 m/s p = 80 kgm/s, south

Write on your note card If you have lost your note card, it is now your responsibility to bring your own note card and add all missing equations (including those from last chapter). p=m∙v m= p/v v=p/m