Subject Assignment | Class Companion

Read the attached passage about how our sense of touch helps us tell the difference between sharp and dull, smooth and rough, and soft and hard objects. Then, answer the questions to show what you have learned. Use complete sentences for short answer questions. Be sure to use evidence from the reading in your answers.

Source 1

When we touch a material, we feel the texture of that material. We can tell if something is hard or soft just by placing our skin on the object. Have you ever considered how we can tell if something is hard or soft? It turns out the answer is deformation due to a contact force!

We learned in Lesson 5 that we can feel objects when the pressure sensors in our skin deform. We also learned these pressure sensors, or force detectors, are all over our body. It is estimated that you have roughly 150,000 of these in each hand! The special sensors for detecting force are called mechanoreceptors. Let’s learn more about how the skin senses different textures and softnesses.

The feeling of sharp vs. dull
When your finger touches a surface, part of your finger deforms. Things that feel sharper deform more of your finger and touch less surface area. Take a finger and touch your desk. Your finger touches the surface and then it starts to deform so that the entire pad of your finger is touching the surface of the desk. Now, take your pencil and use the point of your pencil to touch the pad of your finger. Does it feel different? The reason that the pencil feels sharper is because it makes your finger deform more and less surface area is in contact with the object. The table felt smooth or dull because it did not indent, or deform, your finger as much as the pencil point. The table also pressed on the whole pad of the finger, not just a small area.

The feeling of smooth vs. rough
When you run your hand across different surfaces, some feel smooth and others feel rough. Run your hand across a surface that is rougher, like the stitching on your backpack, a zipper, or the metal part of your pencil. Now run your hand across a surface that is smoother, like the top of your desk or the side of your pencil. Which one had more areas of deformation as you moved your finger across the surface? The rough surface makes many different spots on your finger deform as your finger moves across the surface, and the smooth surface does not have as many spots that cause deformation to the finger on multiple locations. The smooth surface does not deform your finger as much when your finger runs across the surface.

The feeling of soft vs. hard
When your hand touches something soft, the soft item deforms around your finger. The soft surface is deformed due to the pressure of your finger pushing on it. If your finger deforms the surface instead of the surface deforming your finger, it feels softer. Cotton balls feel soft because of how much they deform when we apply pressure. The surface touches a very large part of our fingertips with very little force being applied. Our bodies know when we are applying pressure, and the more we apply pressure without the resistance, the softer an object feels.

How our brains receive the signal
Our sense of soft vs. hard depends on the amount of pressure and deformation on our skin. When the finger is deformed, it sends signals through our nerves to the brain that then interprets the texture of the objects. Our brain turns this signal into information that we can use. — When we touch a material, we feel the texture of that material. We can tell if something is hard or soft just by placing our skin on the object. Have you ever considered how we can tell if something is hard or soft? It turns out the answer is deformation due to a contact force!

We learned in Lesson 5 that we can feel objects when the pressure sensors in our skin deform. We also learned these pressure sensors, or force detectors, are all over our body. It is estimated that you have roughly 150,000 of these in each hand! The special sensors for detecting force are called mechanoreceptors. Let’s learn more about how the skin senses different textures and softnesses.

The feeling of sharp vs. dull When your finger touches a surface, part of your finger deforms. Things that feel sharper deform more of your finger and touch less surface area. Take a finger and touch your desk. Your finger touches the surface and then it starts to deform so that the entire pad of your finger is touching the surface of the desk. Now, take your pencil and use the point of your pencil to touch the pad of your finger. Does it feel different? The reason that the pencil feels sharper is because it makes your finger deform more and less surface area is in contact with the object. The table felt smooth or dull because it did not indent, or deform, your finger as much as the pencil point. The table also pressed on the whole pad of the finger, not just a small area.

The feeling of smooth vs. rough When you run your hand across different surfaces, some feel smooth and others feel rough. Run your hand across a surface that is rougher, like the stitching on your backpack, a zipper, or the metal part of your pencil. Now run your hand across a surface that is smoother, like the top of your desk or the side of your pencil. Which one had more areas of deformation as you moved your finger across the surface? The rough surface makes many different spots on your finger deform as your finger moves across the surface, and the smooth surface does not have as many spots that cause deformation to the finger on multiple locations. The smooth surface does not deform your finger as much when your finger runs across the surface.

The feeling of soft vs. hard When your hand touches something soft, the soft item deforms around your finger. The soft surface is deformed due to the pressure of your finger pushing on it. If your finger deforms the surface instead of the surface deforming your finger, it feels softer. Cotton balls feel soft because of how much they deform when we apply pressure. The surface touches a very large part of our fingertips with very little force being applied. Our bodies know when we are applying pressure, and the more we apply pressure without the resistance, the softer an object feels.

How our brains receive the signal Our sense of soft vs. hard depends on the amount of pressure and deformation on our skin. When the finger is deformed, it sends signals through our nerves to the brain that then interprets the texture of the objects. Our brain turns this signal into information that we can use.

Question 1

Multiple choice

What do mechanoreceptors in our skin help us detect?

Question 2

Short answer

Explain why a pencil tip feels sharper than a table when you touch it with your finger.

Question 3

Multiple choice

Which of the following best describes why rough surfaces feel different from smooth surfaces?

Question 4

Short answer

Describe what happens to your finger and the object when you touch something soft, like a cotton ball. Use evidence from the reading.

Question 5

Short answer

How does your brain know if something is hard or soft when you touch it?

Understanding Touch: Texture and Softness

Question 1

Question 2

Question 3

Question 4

Question 5

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