Momentum is a physics term; it refers to the quantity of motion that an object has. 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 much stuff 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.

Air bag – after car crash and bag has deflated

Collisions, impact (images) – these are situations when a moving object meets another object. It makes a difference which directions the objects are moving, how fast they are going or if one is stopped. If one moving object comes in contact with another object, the result will change the momentum of the objects.

Air bags in cars minimize the effect of the force on an object involved in a collision. In a car collision, the driver and passenger tend to keep moving (Newton’s first law). Their motion carries them towards a windshield. If instead of hitting the windshield, the driver and passenger hit an air bag that has some give. That will result in a significant decrease in force, and the driver and passenger are not hurt – although they are probably pretty surprised.

What’s the problem?

  • Have you experienced momentum? Is it hard to stop when you are running or riding down a hill?
  • What happens if a ball rolls down a hill into a wall? Does it make a difference if the ball is hard or soft?

Engineering ideas

  • mass, motion, velocity, resistance,

Do it
Now it is your turn. Here are some challenges for you to work on…

  • design and build a spinning top out of everyday materials. Top must be able to spin for at least 10 seconds within an area 30 cm in diameter.
  • Coaster Physics (interactive simulation, app, $.99) Design and ride your very own realistic roller coaster, and see how quantities like speed, acceleration, energy and g-force change as you ride along the track.

Learn more…