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) Bell Ringer 1-25-11 See if you can answer these from memory: 1. What is a force? 2. What unit measures force? 3. A ________ is a combination of all the forces acting on an object. 4. List the two types of forces and the key words we use to remember them. Chapter 10 section 2 Gravity Who is this? Issac Newton- He came up with the Law of Universal Gravitation. 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 • Greater the distance, Less the gravity Weight • Weight- the force of gravity on an object or person Free Fall • Free fall- an object is in free fall when there is only one force (gravity) acting on the object 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. • Another name for air resistance is drag. 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? Video • Terminal Velocity 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.
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