Transcript Bell Ringer 1-27-10

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.
2.
3.
4.
Static friction
Sliding friction
Fluid friction
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.