The Mechanics of Sledding

Forces, Friction, and Sledding

How to Achieve Top Speeds & Overcome Friction

Newton's Three Laws:

1) Law of Inertia - An object in motion will stay in motion unless acted upon by an outside force. An            object at rest will stay at rest unless acted upon by an outside force.

2) 𝛴F = ma, where m is mass in kg and a is acceleration in m/s^2

3) For every action there is an equal and opposite reaction

Well, how do they apply here?

Newton's First Law can interestingly enough be demonstrated by the sled hitting the man. This is because the man is unmoving until the sled (an outside force) runs into him.  He is clearly put into motion as he is extravagantly tossed into the air.

The Second Law would allow us to determine the force which was applied from rest if we were given the masses of the men and their sleds as well as their acceleration. Let us pretend that this takes place on a flat surface and that friction is negligible  If each man and their sled weighed 70kg and their acceleration was found to be 3m/s^2 this unknown force could easily be found using 

𝛴F = ma → F = 70(3) → F = 210 N

Also, since this shows that Force and acceleration are proportional, a greater force will yield a greater acceleration, allowing one to go faster. 

Newton's Third Law may not be as apparent due to how fast the sleds are going, but as the sledder makes contact with the man standing still, the force which he exerts on the man is reciprocated with the force which the man exerts on him. However, since he puts the man into motion, the force which he applied was able to overcome the force which the man exerted back on him. 

Friction:

When people think of ice and snow, they often do not think of friction. Although it does appear that objects are able to effortlessly glide over these surfaces, friction is still present. The slipperiness just reveals that the coefficient of friction (μ) is probably lower. 

"Friction Always Opposes Motion"

Therefore, if one is trying to achieve a high speed, such as in the sport of skeleton, the force which the person exerts to propel themselves forward must be greater than the force of friction applied by the ice. Those involved in this sport are constantly looking for ways to complete a run with as little friction as possible.

Sledding Downhill & Forces on an Incline:

More often than not, sledders choose to sled downhill, or on an incline. All three laws of motion, as well as friction, apply in these scenarios as well. 

This diagram shows all of the forces acting on the sled: 

• Gravity - acts straight down, given by mg
• Normal - acts perpendicular to sled, noted as N
• Friction - acts opposite the sleds motion, written as f  *remember f=μN

As soon as sledders are able to overcome static friction, they allow gravity to propel them the rest of the way. 

________________________________________________________________________________

Sources:

Greenemeier, Larry. “U.S. Olympic Skeleton Team Studies Sled Forces in High-Tech Simulator.” Scientific American, 15 Feb. 2010, www.scientificamerican.com/article/olympics-skeleton-vancouver/.

Elliot, Danielle. “Team USA's Bobsled, Luge and Skeleton Get High-Tech Tune-Up.” CBS News, CBS Interactive, 7 Feb. 2014, www.cbsnews.com/news/winter-olympics-2014-team-usa-bobsled-luge-and-skeleton-get-high-tech-tune-up/.