Forces
Matter and energy interact in many ways to keep the Universe changing. Matter and energy are transformed during these interactions producing diverse physical and chemical processes.
A force is an action exerted on a body to change its state of rest or motion.
1. Friction is the rubbing force between two surfaces. The texture of the surfaces will affect the friction. Resistance is the force exerted by a fluid on a body.
2. Gravity is the pulling force exerted by a celestial body over the masses around it or in its surface. Gravity varies according to the size of the celestial body. That's why your weight will be different on Earth and in the Moon. Gravity on Earth is calculated as 9,8 m/s2.
3. The normal force is the upward force exerted by a surface to support the weight of a body.
Force is measured in Newtons. A newton is the amount of force required to give 1 Kg of mass an acceleration of 1 m/s2.
Mass and weight are two different things. Mass is the amount of matter an object has, and weight is the force exerted by the object due to gravity.
Try this...
Physics is a game. Search in your toys and pick some of them.
Friction:
1. Build three tracks by using cardboard and sandpaper. The third one can be with the tiles of the floor, or a smooth surface such as a table. Use masking tape to label each one.
2. Use a metric tape to measure the lenght of the tracks. Be sure they are the same lenght.
3. With a watch or a chronometer, take the time it takes for the car to run through the tracks, and measure the final distance it runs on each one. Be sure that you push the car with the same strenght.
4. Which track was the most effective? Why do you think so? Why do you think that the cars of the Formula 1 must use a special type of tires according to the race and the track?
Gravity:
1. Use a string, a tall structure, such a bench or table and your toy car.
2. Use a scale to measure the mass of the car and a metric tape to measure the lenght of the string and the bench.
3. Tie the car to the upper part of the bench. Leave the car to fall and with a chronometer count the time it takes for it to reach the floor.
You can also do it with two different types of balls. Which one will fall first? The result will surprise you.
Air resistance
1. Use some sheets of the same kind of paper and the same size to ensure the mass and build different types of paper airplanes.
2. Use a metric tape to measure the distance of the place you are going to use as a runway. Be sure that you are in a closed place, so the wind will not interfere with your test.
3. Launch each airplane from the same site and with the same strenght. Measure the distance traveled by each one. Which one went the furthest?
After all these experiments, try to design your own and have fun.
