# Friction

Physics is the science that studies motion and matter and how both work with forces and energy. It is a really big subject that has a lot of different “branches” of scientific study that include motion, sound, waves, electricity, light, sound, and even astronomy.

This science covers the tiniest particles and atoms all the way to the largest objects in the universe.

Friction is what we refer to when one object rubs against another object and causes resistance. Friction acts in the opposite direction and works against the motion.

When an object slides across another object it begins to slow down due to friction. It loses energy, but the energy doesn’t go away. Instead, the energy changes from “moving energy” which is also called “kinetic energy” to heat energy.

We see friction in many of the things that we do every day. Examples of friction can include:

• When you are cold and rub both of your hands together to create warmth.
• When you slide your sled across ice or snow.
• The bottom of a glass that you push across a counter
• The feet of the couch when you slide it across the floor
• Two cards in a deck of cards that slide across each other
• The edge of the sponge when you use it to clean a countertop
• The jeans and your legs when you slide your jeans on
• The pulley and rope that you pull on for curtains or blinds
• The sliding glass door against the other door and the track when you open or close it

Friction that causes heat energy isn’t always a good thing. We have a lot of things in our life that help to prevent friction from happening. The wheel on your bike reduces friction by the rolling action.

Machines need to keep from overheating due to friction, so they use oil, grease, or lubricants. Other ways to keep friction down is by using materials that reduce friction such as the rubber on tires or the metal used for the ice skate blades.

These special materials are said to have different “coefficients of friction” or the ability to keep friction at a minor amount.

### Friction Types

• Dry fiction is when two solid objects touch each other, even if they aren’t moving. That is referred to as “static friction”. If they are moving it’s called “sliding or kinetic friction.”
• Fluid friction involves air or fluid and is the resistance on an object that is moving against the air or fluid. Examples of this include a boat traveling across the lake or an airplane moving through the air.
• Rolling friction happens when a round surface such as a wheel or ball rolls over a surface.

But friction can be very useful! Friction keeps our bodies steady as we walk or run and is helpful when we climb up a hill or even make a fire when we are camping.

### Surfaces Affect Friction

Some materials are smoother or rougher than others and their surfaces can create different friction amounts.

You can see this happen when you ride your bike on a really smooth road and notice that the ride is faster and easier than on a bumpy, lumpy road. Surfaces that have less resistance will let you move faster.

### Friction Factors

When thinking about friction there are two main factors to consider: The surface roughness, which is called the “coefficient of friction” and the force that is exerted between the two objects.

Each one can make a difference in how friction plays out with the results. If you set up a tray and put sand on one half and a number of objects to slide down both the sandy and non-sandy side, you can see that with little effort, the items move down the tilted tray faster on the non-sandy side.

But if you give those objects on the sandy side a harder push that can increase the speed, even with the friction of the sand and the object.

• While the wheels of your bike are great at reducing friction, without friction they wouldn’t work at all.
• Friction keeps everything from sliding and rolling around without control.
• Friction can create static electricity.
• The harder that the surfaces of two objects are pressed together, the more force that is needed to get them to overcome friction and make them slide.

### Q&A

What is the definition of friction?
what we refer to when one object rubs against another object and causes resistance

What are the three types of friction?
dry, fluid, and rolling

What are the two main factors to consider when talking about friction?
surface roughness and force

What important function does friction have in our daily lives?
keeps us and everything else from sliding and rolling around

When you walk across a carpet in winter or dry weather, you are creating friction and this can also create what type of energy that surprises and shocks you?
static electricity