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# Gripper: How Do Ridges on Fingertips Affect The Ability to Pick Up Objects?

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Source:
Author: Janice VanCleave

### Problem

How do ridges on fingertips affect the ability to pick up objects?

### Materials

rubber gloves (the kind used for dishwashing) assortment of small coins

### Procedure

1. Put one glove on the hand you write with.
2. Spread the coins out on a table.
3. Pick each coin up one at a time with the hand covered with the rubber glove. Place each coin back on the table before lifting the next coin.
4. Make note of the ease or difficulty in lifting each coin from the table's surface.
5. Note the texture of the fingers of the gloves.
6. Remove the glove from your hand.
7. Turn the glove that does not fit your writing hand inside out.
8. Put the inside-out glove on your writing hand.
9. Again pick each coin up one at a time with the hand covered with the rubber glove. Place each coin back on the table before lifting the next coin.
10. Make note of the ease or difficulty in lifting each coin from the table's surface.
11. Again note the texture of the fingers of the glove.

### Results

The coins are easily picked up when the glove is right side out, but are difficult or impossible to pick up when wearing the glove inside out.

### Why?

The fingertips are rough when the glove is on properly and smooth when the glove is inside out. The textured tips of the glove act like the ridged skin on the tips of your fingers, the ridges that cause fingerprints. The ridges in the rubber, as well as in your skin, increase friction and allow you to more easily pick up objects. Friction is the resistance to motion between two surfaces that are touching each other. Without the ridges on your fingertips, your fingers would tend to slide over objects, making it difficult to pick them up, just as it was difficult with the smooth tips of the inside-out glove.

### Let's Explore

Does the pattern of the ridges on the fingertips affect their ability to grip surfaces? Repeat the experiment using rubber gloves with different patterns on the fingertips.

### Show Time!

1. Do the ridges on the bottom of your feet increase friction? Use shoes with different sole surfaces such as tennis shoes and leather dress shoes to demonstrate the effect of ridges on friction. Push the shoes across a tiled floor and observe the resistance to motion (friction) of each shoe. Compare the friction of each shoe and label them from greatest friction to least friction. Repeat the experiment on floors with different surfaces. Take a photograph of the bottom of each shoe to display with your evaluation of the amount of friction each type of sole has.
2. How can a klipspringer (a mountain goat) jump and land on an area with about a 2-inch (5 cm) diameter? The hooves of this mountain climber are rubbery and rounded. You can demonstrate the ability of the klipspringer by slowly pitching two basketballs, one properly inflated and the other only partially inflated. Pitch the balls so that they land on a smooth surface. The fully inflated ball will move forward on the surface, but, because of more friction, the partially inflated ball stops when it hits.
3. Dogs slide around on slick floor surfaces. Why are cats not as likely to easily slide on the same surface? Discover how cats can pull their claws back into a sheath and, thus, expose only the soft pads of their feet. Diagrams of the feet of cats with their claws hidden and extended can be displayed.

### Check It Out!

The tarsier (a small mammal) leaps and easily clings to tree branches. The wiry fingers of these animals have pads on the ends that look like a rubber mat. Find out more about this creature and others that can grip well because of a high degree of frictional resistance of their fingers, hooves, or paws. Diagrams of the feet of different animals, indicating the ability of each to grip surfaces, can be displayed.