Hi. This is Tank. Remember me? I’m one of the sled dogs traveling with Dave and Amy. I’m big and strong and I like to pull the toboggans. I was surprised by how the conditions have changed in the past week. I learned all about ice, rocks and friction.
Have you ever slipped on a patch of ice before? What was it like?
We pulled the toboggans to a big lake called Knife Lake. This lake got its name because there is a type of rock here that early people living in the area used to make knives. The rock, Knife Lake Siltstone, forms a sharp edge when it is broken. I could see how it would make handy tools for people.
Anyway, when we were camped on Knife Lake, the weather was warm. It was so warm at night that I didn’t need to wear my dog jacket. The snow melted. I decided to sleep on the bare ground instead of on my dog bed. My sister, Tina, did the same.
We went on a skijoring day trip. That means we pulled Dave, Amy and their friend Conor on skis. We didn’t take the toboggans because we didn’t move camp. I was in charge of pulling Conor. Tina pulled Dave and my mom, Acorn, pulled Amy. I was surprised to find that all the snow had melted on the lake. Even though the snow melted, there is still a thick layer of ice covering up the water on the lake. I found out that ice is slippery! I couldn’t just run like normal. I had to use my claws to grip the ice. When I dig in my claws with every step, I can easily run on the ice. Pulling the people around on the ice was really easy. It felt like Conor didn’t weigh anything.
How do you walk across ice? Do you have anything to help get traction, like Tank’s claws?
During the next day, we traveled with the toboggans. All of us dogs worked as a team to pull the toboggans. Pulling the toboggans on the ice was really easy again. It felt like there was hardly any weight in the toboggans!
When we got to our first portage, we had to travel on land to get from Knife Lake to Vera Lake. We ran up a hill. Suddenly we weren’t on ice, but we were on land. The snow had melted and rocks were exposed. Suddenly, the toboggans felt really heavy. It was really hard to pull the toboggans over rocks compared to pulling them across ice. I looked at Acorn and Tina. We all decided that we needed help, so we stopped to wait for Dave and Amy to help pull the toboggans over the portage. We traveled over more lakes and portages that day. I noticed that each time we were on the lakes, it was super easy to pull the toboggans. Then, when were on rocky or grassy portages it was super hard to pull the toboggans.
I asked Dave why it was so easy to pull the people and toboggans on the ice, but really hard to pull the toboggans on the land. He explained that an icy surface has less friction than a rocky surface. I didn’t know that word, so I asked him what friction is. I thought maybe he meant that they added more weight to the toboggans on the portages and took weight out on the lakes. He said no, the weight was the same. Friction is the force that causes a moving object to slow down when it is touching another object.
So, basically the ice is a slippery surface. Rocks are a rough surface. The toboggans slide easily on the ice, but they don’t slide very well across a rough, rocky surface. I started to pay attention to the different surfaces we were running on. Some of the portages had snow. The snow had more friction than ice, but less friction than rocks. Some places were grassy. The grass had more friction than snow, but less friction than rocks. To sum that up, here is my list going from easiest to most difficult: ice, snow, grass, rocks.
What different surfaces do you walk on in your neighborhood? Make a list like Tank’s, going from less friction to more friction.
Dave told me that we could probably pull more weight than we normally would on the ice, a surface with less friction. We decided to test this out when some people came out to visit us. We loaded up a dogsled with three people. If we tried to pull this dogsled with three people on rocks, it would be impossible and we wouldn’t go anywhere. Sure enough, on the ice, it was super easy to pull three people in a dogsled! Acorn, Tina and I pulled three people all the way across Snowbank Lake! I’m glad Dave taught me about friction and I hope we have more days ahead of traveling on surfaces with less friction.
Additional Information about Friction
Student Response Worksheets