Although rock climbing does not draw large crowds, it claims an annual growth rate of 50%, with women accounting for one-quarter of all climbers. Before beginning, however, climbers should get professional instruction so they understand how to use ropes to protect themselves against the forces of gravity
. Climbers choose nylon ropes because they stretch and absorb the shock of a fall. Good climbing ropes will stretch to double their original length before breaking and have a breaking strength of over three tons of force. Ropes are used in two ways. In "top roping" (the safest method), climbers fix webbing to an immovable object at the top of a cliff--usually a tree or a rock. They attach the webbing to a carabiner
. Then they pass a rope through the carabiner, letting the two ends dangle down the side of the cliff. One end is tied to the climber. The other is tied to and held by a person at the bottom, who keeps the rope taut to stop a fall. Sometimes top roping is impossible because the climb is longer than one-half a rope length or because the climbers don't have access to the top of the cliff to fix the webbing. In that case, someone must "lead climb" and place protection
in the cracks in the rock. The rope is clipped into the protection. The second climber belays
the lead climber. Biomechanics are crucial to climbing. Bones, joints, and muscles combine to provide wedges and levers--all the simple tools necessary to make it to the top. The most sophisticated climbing "gadget" is the human hand. Hand jams allow climbers to grab holds in seemingly impossible places. Climbers also manipulate their center of mass
by working their bodies away from the rock face. This puts more force onto their feet. High-tech climbing shoes make good use of that force. Their rubber soles conform to the surface of the rock and create enough friction (or stickiness) to hold on to steep angles. Climbing techniques put a variety of forces to work. In "face climbing," the most common technique, climbers pull down on handholds and push up on footholds to advance up the rock. By keeping their weight balanced over their feet, the climbers remain stable. In "stemming," climbers push their legs outward against the two opposing rock faces. Their outward push forces their shoes into the walls and the shoes generate an upward frictional force which opposes gravity and allows the climbers to ascend. Climbing is basically applied physics. Grace, rhythm, balance, concentration, and flexibility count more than strength. Although incorrect techniques, bad weather, and misuse of equipment can produce some dangerous situations, climbing is a safe sport when proper procedures are followed.
Friction is the force that causes resistance when we try to slide one surface over another. Friction helps us walk, run, and jump. Without it, a climber would have a very difficult time going up a steep slope. Materials
- a few bricks
- a board or piece of plywood
- two sheets of sandpaper of different grade
- blocks of wood
- gym shoes
- Pull a brick across the board three times, turning the brick each time to use a different face. Is the friction the same for each face?
- Now put one brick on top of another and pull them both across the board. What happens? When you pull the two bricks, you will need to exert twice the effort you needed to pull one brick. Try this with wooden blocks or other materials. You'll find that the ratio of friction to load is the same for identical bodies. It varies, depending on the mass and the surface characteristics of the material.
- Place an object on the board and raise one end of the board. Eventually the object will slide off the board. The higher you can raise the board before the object slides off it, the greater the friction force is between the object and the board.
- Glue sandpaper to a board. Place shoes and other objects on the sandpaper. Raise one end of the board and notice how high you can raise it before the shoes slide off the board. The higher you can raise the board, the greater the friction. Find out whose shoes have the highest friction.
- Place the sole of one of the gym shoes in water and then try to pull each shoe across the inclined board. How does the water affect the movement? Questions
- Look at the soles of several types of gym shoes. What sort of friction devices have been built in?
- Friction creates heat. A rope running through the hands of a climber creates heat. What other examples can you think of where friction creates heat?