Hello my fellow curious critters and welcome back to The Friendly Neighborhood Shark Lady! It feels so good to be back. Now, I know you may be a little confused by the title of this post. You may be thinking, “Alyssa, the Eiffel Tower is an inanimate object. It has been the same for over 100 years. You’re crazy.” You’re right, I am a little crazy, but the Eiffel tower really does grow in the summer and shrink back down in the winter. In fact, it can be as much as 6 inches (15 cm) taller in the summer than it is in the winter all thanks to a little something called thermal expansion.
To understand thermal expansion, we first have to understand atoms, molecules, and states of matter. Everything in the universe is made up of atoms. They are the smallest unit into which matter (aka everything that physically exists in the world) can be broken down into and molecules are groups of two or more atoms. Atoms and molecules are constantly in motion and differences in this motion are what determine what state of matter something is. There are three states of matter: solid, liquid, and gas. In solids, the molecules are tightly packed in a generally uniform pattern. In liquids, the molecules are close together, but there is no regular pattern. In gases, the molecules are spread far apart with no regular pattern. Basically, the faster the molecules move, the more they can expand.
Temperature is a big factor that influences how fast or slow molecules are moving around. When you increase the heat, the molecules will move faster and vice versa. A great way to see this in action is with the different states of matter in water. So if you take an ice cube and add heat it melts into water changing from a solid to a liquid. If you then add more heat to that water, it turns into water vapor changing from a liquid to a gas.
The same amount of heat can impact various materials at different rates. Bonding forces, or the forces that hold the molecules together, vary between different materials. This means that applying the same amount of heat to water and steel could cause the water to evaporate and change into a new state of matter while causing relatively no change to the steel. You can see in the chart below how the same amount of heat impacts different materials.
Thermal expansion, to some degree, impacts everything and can actually cause us some big problems. It can cause the cement in our sidewalks to buckle in the summer heat and crack as it shrinks back down in the winter chill. Over the years engineers have come up with different ways to help combat thermal expansion. In the case of the Eiffel Tower, there are special expansion joints throughout the structure to allow for expansion and contraction with the changes in temperature. These types of joints are commonly used in large structures, like bridges, and dramatically decrease the amount of damage sustained. You can even see the effects of thermal expansion in your own house! I know in my house our front door fits tighter in the door frame during the summer, making it a little bit harder to close than in the winter.
Thank you for coming and learning with me today! I hope you had as much fun learning about thermal expansion as I did. It still blows my mind that it can cause the Eiffel Tower to grow six whole inches in the summer! The world of science is full of amazing things and I can’t wait to learn even more along with you guys. I’ll see you all back here Friday for our weekly dose of sharks!
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