Skiing, Velocity, Acceleration, and Forces

Sir Isaac Newton
Sir Isaac Newton
Back to thinking of physics and skiing.

Newton’s first law of motion states: Every object in a state of uniform motion tends to remain in that state of motion unless there is an application of an external force. This is like a pool of water deep in a mineshaft, it appears 1′ deep, but is actually 30′ or more deep.

By motion we mean velocity which is a vector quantity. That is, we have to consider speed as well as direction. In this discussion we will focus on speed.

You get off of the lift and ski to the start of the run and then stop. Your speed there is 0 and that will not change unless you, someone else, or something else applies force to cause you to lurch into motion. That could be the wind as well as you pushing off.

Acceleration is another vector we often hear of. Acceleration is the change in velocity over time. When you push-off and get headed downhill we all knows what happens, our speed increases and that is an acceleration. That can not happen without a force acting on you. What force is acting on you? The force we call gravity. When you are going downhill gravity provides the force to increase your speed, when going up hill gravity works opposite and provides a negative acceleration (what we often refer to as deceleration) and slows you down.

What other forces act to increase and decrease your speed?

  1. Friction
  2. Friction is a resistive force, it always opposes your motion and is usually thought of as acting between two in-contact surfaces that are moving with respect to each other. The purpose of waxing our skis is to reduce this frictional forces.

  3. Air resistance
  4. Air resistance is similar to friction and is the force that opposes motion, the interaction of our bodies and clothing with the air creates this force. Race suits and tucking both serve to minimize air resistance as well as specially designed poles.

  5. Skidding
  6. Skidding causes your edges to tear the snow and that tearing of the snow acts to reduce your speed. The forces again are resistive and minimize by carving instead of skidding.

  7. Your skis
  8. A skier utilizing proper ski technique will load their skis up with energy and the energy in that ski will give the skier a push to increase their speed. This force I can imagine can work both ways but I can not possibly imagine anyone wanting to go through the pain to release a bent ski in such matter to slow themselves down.

  9. Gravity
  10. As I note above gravity is the primary force causing us to speed down the hill or slow down when we ski uphill.

    Those are the primary forces involved in changing the speed component of your velocity. There are more forces we need to think about skiing and we will discuss those in another post.

Good Stuff!

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