Walking on Ice
Why do we take small steps while walking on ice?
Since ice is slippery, you cannot exert a large horizontal force on
an ice surface without slipping. That makes it easier to fall down.
For example, if you were on ice and starting to fall forward, you
would instinctively try to push backward on the ice. If you do not
slip, by Newton's Third Law (action = -reaction), the ice will push
forward on your feet, helping you to regain your balance. If your
feet slip, you could lose your balance and fall forward.
If you are stationary, you can stay upright as long as your center
of gravity is directly above the area on the ice defined by your
feet and the space between them. By pressing on your toes or heels
and/or your left or right foot, you can keep yourself balanced. If
you take small steps, it is easier to keep this balance and the
corrective forces will be smaller, making it less likely that you will slip.
Keeping your balance is not an easy problem as small children
quickly learn. For example if you are walking on a railroad track
and start to fall to the right, you can regain your balance by
bending the top part of your body to the right or the bottom part (a
foot and attached leg) to the left. Try it!
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
With proper footwear it is not necessary to take small steps, but
regular shoes tend to slip on ice, so the natural tendency is to
take smaller steps to keep our balance and avoid falling should our shoes slip.
This has much more to do with safety than with physics, though
physics is involved in the reasons that we do this for safety. We
take smalls steps for two primary reasons. First is that there is
very low friction between the ice and the sole of your shoe. If you
take small steps, almost all of the force that your foot exerts is
directly down. When larger steps are taken, there is a greater
force pushing forward. Since the friction is low, the forward force
might overcome the downward force and would result in you slipping
and possibly falling and hurting yourself.
The second reason is that if you are on a layer of ice and water
(like a pond) is below that surface, you have to make sure that the
ice does not break. Small steps help reduce the downward force on
the ice compared to running or regular walking. Also if the ice
starts to crack, you can hear it because small steps are
quieter. Taking small steps allows you to test out the strength of
the ice without transferring your full weight to that foot, at which
point it would be too late to step back without breaking through the ice.
So to sum up, we take small steps because of reduced friction and to
reduce the forces that we apply to the ice with our body weight.
Although Ice can be very slippery, it still takes a certain amount
of force to start something like a human foot sliding across it.
Now, imagine a ladder leaning against a wall, If it is at a very
steep angle, the pressure against the wall is minimal. However, if
you lean the ladder at a less steep angle, its force against the wall grows.
Back to the short steps on ice, by taking shorter steps, we are
causing our feet to stay more directly underneath us, like a ladder
leaned very steeply against the wall. This way, we minimize the
sideways force we are exerting on the ice, which hopefully will be
less than what it takes to start our feet sliding. If that fails,
then at least our other foot is pretty close to the direction we're
going to have to put it down in to keep from sliding too far.
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Update: June 2012