A freshly waxed car has low adhesive forces with water, so water beads up on the surface, as a consequence of its cohesion and surface tension. This minimizes the contact between water and metal, thus minimizing rust. Water molecules are attracted in every direction by other water molecules and are more attract- ed to each other than they are to the wax paper.
Beading is essentially created by polymers that create a very high surface tension, meaning water runs off the paint freely reducing streaking and tide marks that might have previously pooled on the paint surface. The end result is a paint surface which is much slicker and easier when washing, drying and detailing. Why do beads of water often form on a slippery surface, such as a freshly waxed car? The attractive cohesive form between water molecules pull them together to form beads.
You just studied 6 terms! Why do water drops bead on a freshly waxed surface? The strong cohesive forces between water molecules attract each other and the result is a sphere, which is squashed down into a bead by the force of gravity. Surface tension allows objects that are denser than water, such as the paper clip shown in B in Figure below , to nonetheless float on its surface. It is also responsible for the beading up of water droplets on a freshly waxed car because there are no attractions between the polar water molecules and the nonpolar wax.
Waxed paper pushes water away and does not absorb it. The surface tension of the water pulls it into a little round blob; these blobs, or drops, can slide around waxed paper because the paper does not absorb it. Why does it work? Water molecules have a strong attraction for each other. This force is strong enough to make the water move towards the water on the toothpick.
But when you dip the toothpick into dish soap, the water water is repelled, not attracted, so the water bubble bursts as it tries to move away. The surface tension of the water pulls it into a little round blob; these blobs, or drops, can slide around waxed paper because the paper does not absorb it. Water "prefers" to stick to itself cohesion more than it sticks to other substances adhesion.
Wet and Dry Printable guide. They were developed and tested with preschool and kindergarten educators. Explore the behaviour of water on different absorptive materials. Per Child: 1 pipette or small sponge 1 piece of waxed paper, about 15 cm x 15 cm 1 piece of smaller regular paper 1 straw. Does the regular paper get wet? What about the waxed paper? Which paper absorbed the water?
Which one did not absorb the water? Where else do you see water drops like this? Details Activity Length 15 mins. Objectives Explore the behaviour of water on different absorptive materials. Complete the other lab activities before coming back to observe the beakers. After observing how the water moved from the full to the empty beakers, use the background information to describe why this happened. What was different between the hot and cold beakers?
When a drop of water is held on a sloped surface, does the water drop slide down or roll down the slope? Write your prediction here. Using one of the water drops on the waxed paper, sprinkle a few grains of pepper over the drop. Tilt the waxed paper and observe the movement of the water drop.
What do you observe? Why do you think this happens? Was your prediction correct? Why or why not? Materials: Beaker of water pipette toothpick waxed paper straw soap solution Procedure: 1. Use the pipette to gently put several drops of the water onto a sheet of waxed paper. Carefully observe the shape of the drops. Describe the shape here. With a toothpick, try to cut one water drop in half. How many smaller drops can you make? With a drinking straw, blow gently to try to put two water drops together.
Do they rejoin? Dip the end of the toothpick in soap solution. Poke the water droplet with the soapy tip. Describe what happens to the drop. The cohesive force of water pulls the water molecules toward each other forming a drop. The molecules in the outer layer are drawn in toward the center of the drop, giving the drop its round shape.
The surface tension that holds the water in that shape affected how the water acted when you pushed on it with the toothpick and the straw. Activity 4: How many water drops can fit on a penny? Take a Guess: How many drops of water can fit on one side of a penny?
Each group should get one penny per person for the testing. Rinse each penny in tap water and dry completely with a paper towel. Place the dry penny on a flat paper towel. Count the number of drops for each student testing and record in the data table. Repeat Steps 1 - 4 for each group member before calculating your average.
Student 1 Student 2 Student 3 Student 4 Average of drops of water drops Answer each question related to the experiment. Using the terms of cohesion and surface tension, explain what happened in the experiment. How do your results compare to the other groups in your class? Provide at least 2 possible reasons for any similarities and differences you identified between your data and others data.
You just saw three important forces tugging on the water: gravity, cohesion, and adhesion. Gravity pulls down on the drop causing it to flatten the droplets, cohesion attracts the particles to each other and holds the droplets together, and adhesion attracts the drops on the surface of the coin.
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