A Closer Look at Forces

Remember:Good readers ask questions as they read to clarify their understanding and to find out more about a topic. As we read though this information, try to be an active reader – ask yourself questions and picture forces in your mind!

Fundamental Forces

•Gravitational force• Electromagnetic force• Strong nuclear force•Weak nuclear force

Gravitational Force

• What goes up…must come down!• Force that pulls objects to the ground• All things that have a mass, have a

gravitational force• Force is very weak when object mass is small• Gravity is NOT responsible for many of the

movements that we experience in everyday life…except for things falling to the ground!

Electromagnetic Forces

• Responsible for MANY of the motions and activities we deal with on a daily bases

• Often we don’t realize this because we have SO many different names for these forces

Pull on the earth

Magnetic pull/push• Static cling• Static electricity• Force of an electric current• Force of lighting

• Muscular force• Hurricane force• slapshot

Frictional force – force of resistance

Representing Forces

• Forces have 2 components

–Magnitude

•Direction

Magnitude

• A measure of how STRONG the force is

Direction

• Refers to which WAY the force is pulling or pushing

• In diagrams, forces are usually represented by arrows

• Head of the arrow refers to the direction of the force

• The length or thickness of the arrow refers to the magnitude

• The unit we use to measure force is the newton (N), named after Sir Isaac Newton – he discovered many of our current ideas about force and motion.

Mass and Weight

• Mass is a measure of the amount of matter or material in an object

• Weight is a measure of how strong the force of gravity is between two objects

• Check it…Mrs. Hurren has an example for you…

• The Earth exerts a force of 9.8 N for every kilogram of an object’s mass

• So we say on Earth, the force of gravity is 9.8 N/kg (9.8 newtons per kilogram)

• The Moon has much less mass than Earth, so it’s gravitational pull is less…only about one-sixth of the Earth's gravitational pull.

• Although your mass doesn’t change if you were to go to the moon, your weight would only be one-sixth your weight here…cool!

Closer look at Friction

• Friction is the force that resists motion between two objects in contact with each other

• We NEED friction!• It allows us to walk without slipping and keeps

things from sliding off surfaces• Every day lives are saved by friction when

brakes are applied to the wheels of cars, trucks and bikes.

Static Friction

• The force that prevents surfaces at rest from sliding against one another

• Check it! Mrs. Hurren has ANOTHER example for you…

• Once the book begins to slide, sliding friction is the force that acts against the movement and causes the book to slow and stop.

• Sometimes we want to minimize friction• When 2 surfaces rub together in a system, the

rubbing can cause the system to overheat and prevent it from working smoothly

• It can also cause parts to wear out quickly

• Watch out for unwanted friction with your Goldberg assignment…!

• Smooth surfaces cause less friction than rough ones, but there is ALWAYS friction whenever 2 surfaces attempt to slide across one another!

• Where do we see friction in our everyday lives?

Check Your Learning

• State 2 components common to all forces. How are these indicated in a diagram?

• Name 3 forces involved in brushing your teeth.

• How does learning about forces help with your design of your Goldberg masterpiece?

Special Treat!Friction is hilarious…