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Answer Your Own Question...
How does a curling rock run down a sheet of ice? |
| Answer Your Own Question... How does a curling rock run down a sheet of ice? Curling is a complex sport played on ice which involves throwing rocks at circles which are called houses. At first glance it may seem simple but he forces of the game are complicated. The Ice Surface and Rock Surface The ice surface is created differently than hockey ice in order to diminish some of the forces of friction. The pebble or little bumps of water are added to the ice in order for the rock to glide much more easily across the surface of the rink. This creates less friction by diminishing the surface area in which the rock and ice are in contact. These properly put on bumps create the rock to bounce and skid across the top of the pebble creating less contact and thus less friction. The rock is also crafted to lessen frictional forces by making it so that only a small percentage of the bottom of the rock actually touches the pebble. The bottom of the rock is built so that only a raised ring glides across the ice. (See Figure 1) Figure 1 Bottom of rock What causes curl? Angular and Linear Speed The cause of curl on a rock is because of the velocity vectors present on the rock. There is a linear velocity vector that is going straight and an angular velocity vector which is present towards the centre of the rock. These velocity vectors put together cause the rock to have more friction on one side of the rock causing it to curl. The turn that you put on the rock when you throw it is the determining factor onto which side of the rock has increased friction. If you throw an inturn both velocity vectors are working towards the left side of the rock and the only vector working towards the right is the linear velocity vector (as if you are throwing the rock). Thus the side with more velocity is pushing the rock or making it curl towards the side with the lower velocity. (See figure 2) Figure 2 Sweeping There is much debate onto why sweeping works. There are three main theories on why sweeping works. The first is that it increases the temperature of the ice making the ice temporarily melt allowing the rock to glide more easily down the ice. The second theory is that sweeping gently polishes the pebble on the ice making it easier for the rock to glide along the ice because of decreased friction. (See figure 3) Figure 3 The third and least common theory is that sweeping bends the lattice structure of the ice making a flatter surface that the rock can slide on more easily. All three theories would also support the reason why sweeping makes the rock curl less. By increasing the linear velocity vector and keeping the angular velocity vector the same the rock will curl less because the left and right velocities would be closer to the same lessening the difference in force of friction. This also is the reason for rocks curling more near the end of their journeys because their linear velocity has decreased and the angular velocity has stayed the same. The most probably accurate theory is that the force of friction is diminished due to polishing of the pebble. There have been studies to show that sweeping does not increase temperature enough to change ice to water. The lattice theory was not backed with significant evidence and only appeared in one source. Sweeping is effective if a great deal of force is supplied to the broom while oscillating it at a constant speed. If you merely press and drag the broom with a great deal of force it will not polish the pebble it will just break off large tips on the pebble. If the broom is lightly brushed back and force it will not have the force needed to polish the pebble. Thus, an equal distribution of the two techniques is most useful. Momentum and Rocks In a game at least once an end the skip will usually call a take out. Using the law governing conservation of momentum we can predict where the rocks will go and at what speed they will move at give the original speed and where the rocks are hit. (See Figure 4) In Conclusion, there are a variety of forces that are present on the curling ice. It is a fascinating topic and many hours could be spent analysing the many facets of the physics of curling. |