1. Light always travels in straight lines. It will NEVER curve.
Light sources
How light travels
Light travels in straight lines. If you want to prove this, look at a beam of light coming from a small torch, or find a tube or hose. You can see through the tube when it's straight, but if it's bent, you can't see anything.

2. Background about Reflected Light
Light moves very, very quickly—at 186,282 miles per second, or 299,792,458 meters per second. Light rays travel in one direction until they hit an object. Light reflects, or bounces off the object and into our eyes so we can see it. The object also absorbs, or takes in, some light. Objects that are shiny, such as metal pots and mirrors, reflect light better than dull objects such as dark sweaters or fuzzy toys, which absorb more light. Smooth, flat mirrors reflect light in roughly the same angle the light hits them so we can see reflections. When light hits curvy mirrors, it bounces off in many different directions and back to our eye. We see our reflections, but they are distorted.

3. Reflected light For us to see things, light has to travel from its light source to the object and then bounce off it into our eyes. We can't see behind us because the light that reflects off the things behind us doesn't make it into our eyes. Shiny smooth surfaces reflect light well. (Examples: TV, mirrors, CDs, spoons, etc.)

4. When you think of reflection, think of BOUNCE
When you think of reflection, think of BOUNCE. Light bounces off a shiny surface at the same angle it hits the shiny surface.
Mirror

5. REFRACTION: Light rays usually travel in straight lines, but when they pass from one material to another they can be forced to bend (change direction and continue on a new straight path). The bending is called refraction. It happens because light travels at different speeds in different materials. If light rays travel through air and enter a more dense material, such as water, they slow down and bend into the more dense material. Light rays moving into a less dense material, such as from water to air, speed up and bend outwards.
Light
Notice the light coming from the air into the water gets bent as it enters the water. It bends again as it exits the water.

6. Refraction (Think BEND)

7. Refracting white light with a prism
When you think of refraction, think of BEND. During refraction, light bends as it enters and exits a medium.

8. Refraction example
Straw in a beaker of water. The straight straw appears to be bent or broken as the light rays are refracted (bent) at the boundary between the air and the water.

9. SOME Common objects that refract light
Eyeglass lenses
Microscopes (because of lenses)
Telescope (because of lenses)
Hand lens (magnifying glass)
Prism
Water drops when they form a rainbow

10. Opaque, Translucent, and Transparent
Light can easily pass through some objects, such as clear plastic or glass. These objects are transparent and we can see through them. Light cannot pass through opaque objects, such as wood blocks. Objects that block light can cast shadows. Show children that when an object blocks light, light cannot pass through to the other side. You see a dark spot that’s shaped like the object—a shadow. This is how we know that light travels in straight lines; if it curved, it would bend around opaque objects and shadows would not be made. Some objects block some light but also allow some light to pass through. Sunglasses and stained glass block some light. Translucent objects diffuse light in many different directions. It is difficult to see through translucent objects (only allow a little bit or light to pass through) such as sheer fabric, wax paper, frosted glass, or tissue paper.

11. Light Family Activities – Feel Free To Try
Reflection
Together with your child, look for your reflections in different objects in your home. You can find your reflection in tea kettles, pots and pans, mirrors, and metal pipes and tools. If you take a walk, your child will see his or her reflection in car doors, and in shop windows. Remind your child that when a light hits a smooth, flat object like a mirror, it bounces back in roughly the same direction. When light hits a bumpy object, it bounces back in different directions. As a result you see a distorted or “funny” reflection. Experiment looking at your reflection in different surfaces and feel free to make funny faces!
Passing Through
Remind your child that light can pass through some objects, but can’t pass through others. Some objects block some light and let some light through. Gather different objects and have your child predict if the object is opaque, transparent, or translucent. Choose a variety of objects such as wooden blocks, a glass, or tissue paper. Then use a flashlight to shine on the object to test your child’s predictions.
Can You Grab It?
Collect a bunch of small objects of different shapes and sizes. Then fill a few big glass bowls or wide glass vases with water. Drop the objects into the containers. Challenge you child to grab the objects while looking at the bowl from above, and then from the side. Discuss how light refracts and bends when it passes from air to water, so this challenge might be trickier than your child expects because the objects may look like they are in a different location, or even as if they are broken.