Surface Tension1. What is surface tension?2. How is surface tension important in

nature?

Friction1. What is friction?2. How does friction affect motion?3. Give examples of how we use our

understanding of friction in our daily life.

Gravity1. What is gravity?2. Why is gravity important in our universe?

Cite 3 examples. 3. What could possible happen if our earth

suddenly loses its gravity?

Air Resistance1. What is a “drag”?2. How does air resistance affect the motion

of falling bodies?3. Why is it important to understand the

concept of “drag” when designing cars and planes?

Magnetic Force1. What is magnetic force?2. What could possibly happen if the earth

loses its magnetism?

Buoyant Force1. What is buoyant force?2. How do ships and submarines use

buoyancy to travel in water?

Name of Force

Definition Examples

Gravity Gravity is a force that attracts bodies of matter toward each other. It is a force that is everywhere there is matterThe size of the force depends on two factors: mass and distance

-Force of attraction increases as mass increases-Force of attraction increases as distance decreases

Keeps the planets in orbit around the sun, moon in orbit around the earthHolds us to the earth's surface. Weight is a measure of the force of gravity on your massIs responsible for the tides.Causes acceleration of a falling objectResponsible for air and water pressure (weight of air and water!)

Name of Force

Definition Examples

Surface Tension

Liquid molecules are attracted to each other (some more than others!)Attraction between molecules causes a “membrane” to form on the surface of liquids

Allows small insects to walk on waterMosquitoes “attach” eggs to surface of waterSoap, kerosene, can “break” the surface tensionBlowing bubbles – stretching surface tension

http://www.youtube.com/watch?v=45yabrnryXk&feature=fvw

Magnetic An invisible force felt within the space around a magnet.  This space, called the magnetic field, can either attract (pull) or repel (push away) other magnets and some types of metal.All magnets have two poles. These poles are opposites and are called the north and south poles.  Opposite poles attract, while like poles, repel.

Compasses work because of Earth’s magnetic fieldIron and Nickel can be magnetized - Other metals cannotMagnets can be made with electricity.

Electrical

A force between two charged particlesOpposite charges attract, while like charges repel.The size of the force depends on two factors: size of charge and distance of objects

-Force of attraction/repulsion increases as the size of the charge increases-Force of attraction/repulsion increases as distance decreases

Static Electricity caused by touching or rubbing of two surfaces which causes buildup of charges Walking across carpet – you gain electrons which are released when you touch a doorknob (attracted because it is more +)!

Turning Force

causes an object in uniform circular motion to move toward the center of the circular path.

a car making a turn the movement of a roller coaster

When you are riding in a car and the car accelerates, your body tends to move backward against the seat. Likewise, if the car stops suddenly, your body tends to move forward, in the direction of the dashboard

Buoyant Force (Upthrust)

Force equal to the weight of the fluid (liquid or gas!) that is displaced

by the object.Determined by an

object’s DENSITY (mass ÷ volume!)

An object will float ifDensity of Object <

Density of Fluid

Equal to the weight of the fluid (liquid or gas!) that is displaced by the objectExplains why ships don’t sink Why we only see about 10% of icebergs (“tip of the iceberg”)

Friction A force that acts in a direction opposite to the motion of a moving object.Friction will cause a moving object to slow down and finally stopDependent on two factors

-How hard surfaces are pushed together-The materials of which the surfaces are made

Sliding friction – when solid objects slide over one anotherRolling Friction – produced by wheels, ball bearings, etcFluid (liquid or gas!) Friction – when an object moves through a fluidLubricants reduce friction

Friction is a force that resists motion. It involves objects that are in contact with each other.

Cause of frictionCause of friction: Some scientists believe that friction is caused mainly by the uneven surfaces of the touching objects. As the surfaces are rubbed together, they tend to interlock and thus offer resistance to being moved over each other. It has been shown that tiny particles are actually torn from one surface and become imbedded in the other.

Factors affecting Friction

The only factors affecting friction is the amount of mass and the nature of the surface. The surface area and the speed the block is pulled should not matter.

1. Friction acts parallel to the surfaces that are in contact and in the direction opposite to the motion of the object or to the net force tending to produce such motion.

2. Friction depends on the nature of the materials in contact and the smoothness of their surfaces. The friction between two pieces of wood is different from the friction between wood and metal.

3. Sliding friction is less than or equal to starting friction. Starting friction prevents motion until the surfaces begin to slide. When the object begins to slide, less force is required to keep it sliding than was to start it sliding.

4. Friction is practically independent of the area of contact. The force needed to slide a block

along a table is almost the same whether the block lies on its side or on its end. The surfaces are in contact in more places when the area of contact is large, but the pressure is greater when the area is small.

http://www.fearofphysics.com/Friction/friction.html

"Drag" (sometimes called air resistance or fluid resistance) refers to forces that oppose the motion of a solid object through a fluid