Forces in Motion

   What do race car drivers and luge drivers have in common?  They both want to control a push or a pull that can move, stop, or change the speed or direction of an object.  This is called a FORCE.

  A race car or a luge starts to move, stops moving, or changes speed or direction only when a force acts on it. Some forces act on objects directly.  When you push on a door, you directly apply the force that makes the door open. Other forces, such as gravity and magnetism, act on objects at a distance. 

   Three of the forces that affect objects on Earth every day are friction, magnetism, and gravity. Two other types of forces are air resistance- drag and contact force. 

Let's look at each of these forces in more depth and do several online experiments with these forces. First, let's learn a little more about these forces and take an online quiz.

http://www.bbc.co.uk/schools/gcsebitesize/physics/forces/forcesandobjectsfhrev2.shtml

 I. FRICTION

  Friction is a force that opposes, or acts against motion when two surfaces rub against each other.  When a baseball player slides into second base, the friction of his or her legs rubbing on the dirt provides enough force to stop the slide.  However, a luge, or a sled on ice keeps moving for quite a while.  There is very little friction from ice. 

Experiment with friction by using different road surfaces to push a car. Then, take the quiz.

http://www.bbc.co.uk/schools/scienceclips/ages/8_9/friction.shtml

II. AIR RESISTANCE-DRAG

  When an object moves through the air, the force of air resistance or drag acts in the opposite direction to the motion. Air resistance depends on the shape of the object and its speed.  An example of air resistance would be a parachute attached to a person flying through the air, or a parachute attached to a race car to reduce its speed.

Reduce or increase the speed of the truck by adding weights and/or parachutes.  Then take the quiz.

http://www.bbc.co.uk/schools/scienceclips/ages/10_11/forces_action.shtml

III. GRAVITATION

  Gravitation is the force that pulls all objects in the universe toward one another.  This is the force that holds things to the surface of the Earth. Even two ping pong balls sitting side by side on a table pull on each other with gravitation. The force of gravitation acting on them is smaller than the force of friction keeping them apart, so the balls don't move towards each other.

   Earth and a Ping Pong ball pull on each other with a much stronger force, so they can stay together. This is because the strength of the gravitation between two objects depends on the mass of the objects. The total mass of two ping pong balls is small, so the force between them is small. The total mass of a Ping Pong ball and the Earth is very large, so the force between them is much larger.

What does gravity do?

http://ology.amnh.org/astronomy/gravity/pages/gravitydo.htm

 Design your own roller coaster using the forces of gravity and friction.  How fast can you make it go?

http://www.funderstanding.com/k12/coaster/index.html

  Here is an experiment that you can try at home called Galileo's Free Fall.

http://www.spartechsoftware.com/reeko/Experiments/gravity.htm

Journey into space to take the Gravity, Orbits, and Collisions challenge.

http://teacher.scholastic.com/activities/explorations/space/level2/interactive.htm

Do you want to look like you are defying gravity?  How do the magicians appear to float in the air.  Here's the trick.

http://www.exploratorium.edu/snacks/anti_gravity.html

IV. MAGNETISM

  Another force that affects us every day is magnetic force, or magnetism. Magnetism is the force of attraction between magnets and magnetic objects.  Every magnet has two poles. A bar magnet hanging from a string will turn so that one end points north and one end points south. The end that points north is the magnet's north-seeking pole.  The end that points south is the magnet's south-seeking pole.

  Every magnet has a magnetic field around it. You can think of a magnet field as lines of force that run from the north-seeking pole to the south -seeking pole of the magnet.

 Why do a magnet's poles point north and south? It's because Earth is a huge magnet. On Earth the magnetic north and south poles are about 1500 km (930 miles) from the geographic North and South Poles. Earth's magnetic field causes the needle of the compass to point north and south.

Here is an experiment that you may be interested in. You can make a magnetic field that is stronger than the Earth's.

http://www.exploratorium.edu/snacks/circles_magnetism_I.html

Here is an online activity with a magnetic field of a bar magnet.

http://www.walter-fendt.de/ph14e/mfbar.htm

Magnets and springs activity.

http://www.bbc.co.uk/schools/scienceclips/ages/7_8/magnets_springs.shtml