Friction Force
- Friction is the force acting between two rough surfaces when they slide over each other.- Friction is a force that opposes motion.
Advantages of force of friction
- Friction enables us to walk without sliding.- Friction helps in lighting a matchstick when rubbed against matchbox.
- Friction helps in rubbing the board.
- Friction helps in sharpening or filing cutting tools.
- Carpenter uses sandpaper to smoothen rough surface.
Have you ever tried to walk outside on mud after it has rained? It is usually very difficult. This is because the mud is slippery and it reduces the friction between our feet and the ground.
Disadvantages of force of friction
- Friction produces unnecessary heat leading to wastage of energy.- Friction wears out shoes and tires due to the contact with earth surface.
- Friction makes work or movement difficult.
Ways of increasing friction
1. Increasing force between surfaces.2. Creating a rough point of contact that is why the shoe soles and car tires are rough.
Ways of Increasing Friction - Image Courtesy
The bottom of our shoes and cars' tired are usually rough to increase friction with the ground.
The bottom of our shoes and cars' tired are usually rough to increase friction with the ground.
Ways to reduce friction
1. Making the surface smoother.2. Lubricating. This is oiling or greasing moving parts.
3. Streamlining bodies such as cars or airplane.
4. Using ball-bearings.
While cars have treads (deep wavy lines on a tire's surface) tires to increase friction with the ground, their bodies are shaped in a way to reduce with the air. This is know as reducing a car's drag.
A Non-Streamlined Object
The object experiences a lot of friction with the air.
The object experiences a lot of friction with the air.
A Streamlined Car
The car has a sharp front to reduce its friction with the air which can reduce its speed.
The car has a sharp front to reduce its friction with the air which can reduce its speed.
Light Energy
Reflection of light
- Reflection of light is when light falls on a surface and the light rays bounce back.- Reflection of light when it falls on different materials.
- Reflection of light takes place when light falls on a shiny smooth opaque surface.
- Examples of opaque materials that cause reflection are mirror and smooth shiny surfaces.
- When light is reflected in one direction on smooth surface the type of reflection is called regular reflection.
Regular Reflection
- The type of reflection is called irregular reflection.
Irregular Reflection - Image Courtesy
Application of reflection of light in daily life
1. A microscope uses a mirror to reflect light to the specimen under the microscope.2. Car mirrors enable the driver to see things behind the cars.
3. Reflection enables one to check how they look.
4. Reflection facilitates the dentist checking in your mouth.
5. Reflection is used when making a periscope. A periscope is used to observe objects round corners. It is also used by sub-marines to observe vessels in the sea.
A Periscope
Reflection in a Periscope
Machines ( Slopes)
- Any flat surface can be referred to as a plane.- A slope is an example of an inclined plane.
- Inclined plane makes work easier by reducing the effort required to perform a certain task.
- Examples of inclined planes that make work easier are ramps, ladder, staircase, road winding uphill.
1. Staircase as an inclined plane
- Staircase makes it easier for a person to move to another part of a building or a room.2. Ladder as an incline plane
- Ladders are used in construction sites to move to a higher level.- They make work easier by reducing the effort when climbing.
3. Ramp as an inclined plane
- Ramp is a flat plane. It is used when moving from the low point to an upper part.- Ramps are necessary in most building because they are easier for physically challenged people to move to the upper part of the building easily.
Important tips
- Machine makes work easier.- A ladder is a simple machine that makes work easier.
- A ladder belongs to a group of machines called slopes.