Bell Ringer 1-27-10

See if you can answer these from memory: • What is a force?

• What unit measures force?

• A ________ is a combination of all the forces acting on an object.

• List the two types of forces and the key words we use to remember them.

Chapter 10 section 2 friction and Gravity

Friction Foldable

• Once your paper is folded, label the four sections with the four types of friction: 1. Static friction 2. Sliding friction 3. Fluid friction 4. Rolling friction p. 342

Types of friction

• Static friction – friction that acts on objects that are not moving Ex. Pushing on a heavy refrigerator/ driving off with a book on top of the car • Sliding friction – friction that occurs when 2 solid surfaces slide over each other Ex. Bike brakes/ ballet dancers

Types of Friction (cont’d)

• Rolling friction- occurs when an object rolls across a surface (ex: skateboard on road) • Fluid friction – occurs when a solid object moves through a fluid (ex: surfboard on water)

Who is this?

Sir Issac Newton

Gravity

• Gravity- a force that pulls objects toward each other – Ex: Earth pulling us toward it • Law of Universal Gravitation- the law that states that the force of gravity acts between all objects in the universe • Why don’t you feel the gravity between other objects and you?

Gravity

• Two factors affect Gravity: – 1. Mass • amount of matter in an object • Not affected by gravity • Greater the mass, greater the gravity • Ex: sun and planets – 2. Distance • Increase distance, decrease gravity

Weight

• Weight- the force of gravity on an object or person

Air Resistance

• Air Resistance- an upward force exerted on falling objects • It’s not the same for all objects.

• The greater the surface area, the greater the air resistance.

Terminal Velocity

• Terminal Velocity- the greatest velocity a falling object reaches – Exists when the force of air resistance equals the weight of the object/or the force of gravity pulling down on the object – Air Resistance = Weight or Gravity

Projectile

• Projectile- an object that is thrown • Will an object that is thrown horizontally land on the ground at the same time as an object that is dropped?

Exit Quiz 1-26-10

1. What is a force?

2. The combination of all the forces acting on an object is called ______.

3. If two forces are balanced, is there a net force?

4. The SI unit for force is the ________.

5. Tell me one of the four types of friction and give an example.