Unit 2 Chapter 7 Lesson 2 Friction and Gravity p

Objectives  SW describe friction and identify factors that determine the friction between two objects.  SW identify the factors that affect the gravitational force between two objects.

GLEs  17 Describe and demonstrate that friction is a force that acts whenever two surfaces or objects move past one another.  19 Identify forces acting on all objects  20 Draw and label a diagram to represent forces acting on an object.

Ignite! videos  Topic 6: Fun with Friction and Direction of Friction Force  Topic 3: Fun Understanding Gravity and Force  Gravity Song

Vocabulary  Friction = the force that two surfaces exert on each other when they rub against each other.  Sliding friction = friction that occurs when two solid surfaces slide over each other  Static friction = friction that acts between two objects that aren’t moving  Fluid friction = occurs when a solid object moves through a fluid  Rolling friction = friction that occurs when one object rolls across a surface

Vocabulary (continued)  Gravity = force that pulls objects toward each other  Mass = the measure of the amount of matter in an object (kilogram)  Weight = a measure of the force of gravity on an object

My Planet Diary  Space Athletes Have you ever seen pictures of astronauts playing golf on the moon or playing catch in a space station? Golf balls and baseballs can float or fly farther in space where gravitational forces are weaker. Training flights prepare astronauts to work with the lack of gravitational force.

Ignite!  Students will watch videos and interact with questions and answers.  Topic 6: Fun with Friction Directions of Friction

Lab Resource  Observing Friction Activity Pass out bags of various items to test friction 1 bag per group of 4 Feel / rub each item in bag Organize the items from little or no friction to great amount of friction. Write the order of your items on paper. Write names of people in group and date.

What Factors Affect Friction?  Two forces that affect the force of friction are the types of surfaces involved and how hard the surfaces are pushed together.  Example: Football player pushing a blocking sled. If the material on the bottom of the sled is changed, then the sled may be harder to move.

 A heavier sled would be harder to push.  Friction is increased when surfaces push harder against each other.  Example: rubbing hands together  Friction acts in a direction opposite to the direction of the object’s motion.  Without friction, a moving object will NOT stop until it strikes another object.

Teacher Demo  Materials: 2 books, string, elastic band, several round pencils  Stack 2 books together. Tie a string around the bottom book. Attach an elastic band to move the books. Now place several round pencils under the books, and pull the elastic band.  What did you observe?

Questions  Why is it more difficult to walk on ice than on the floor?  How is friction between people like friction between objects?

Types of Friction  Sliding friction  Static friction  Fluid friction  Rolling friction

Sliding Friction  This is what makes objects slow down and stop.

Static Friction  When you try to push an object across the floor and can’t  When you can move it there is no more static friction.

Fluid Friction  Fluid friction is easier to overcome than sliding friction.  This is why sidewalks become slippery when wet.

Rolling Friction  This is easier to overcome than sliding friction.  It makes it easy to push a bike when the wheels turn, but hard to push if you have the brakes on.

Spinning Plates  Materials: 2 identical pie plates per group, marbles  Stack 2 pie plates together and try to spin top plate. Separate the plates and place marbles in the bottom of the plate. Place other plate on top of marbles. Try to spin top plate. What did you learn?

Apply It!  Your family is moving and isn’t sure how to best overcome friction while moving furniture. You have a spring scale, wood blocks to represent your furniture, and sandpaper, aluminum foil, marbles, and olive oil as possible surfaces to slide your furniture over.  In a group of 4, design an experiment that will help you determine which material will reduce friction the most.  What would you expect to learn from this experiment?

Ignite! Videos  Students will watch videos and interact with questions and answers.  Topic 3: Understanding Gravity Force Gravity Song

What Factors Affect Gravity?  Sir Isaac Newton concluded that a force acts to pull object straight down toward the center of Earth.  Therefore, a skydiver will be pulled to Earth.

Universal Gravitation  Gravity acts everywhere in the universe.  This force makes skydivers fall to the ground.  It is the force that keeps the planets orbiting the Sun.  Law of Universal Gravitation = the force of gravity acts between all objects in the universe that have mass

Factors Affecting Gravity  A gravitational force exists between two objects in the universe.  Two factors affect the gravitational attraction between objects; mass and distance.  The more mass an object has, the greater the gravitational force between it and other objects.  Gravitational force also depends on the distance between the objects’ centers.

Weight and Mass  Mass is confused with weight.  Your mass is the same on Earth as it would be on any other planet.  If you were on the moon, you would weigh about 1/6 of what you would weigh on Earth.  On Mars, you would weigh 1/3 of what you would weigh on Earth.

Lab Resource  Calculate your weight if you were on the Moon? Mars?

Ignite! videos  Sw watch any other videos that correlate with friction and gravity,

Objectives  SW describe friction and identify factors that determine the friction between two objects.  SW identify the factors that affect the gravitational force between two objects.

GLEs  17 Describe and demonstrate that friction is a force that acts whenever two surfaces or objects move past one another.  19 Identify forces acting on all objects  20 Draw and label a diagram to represent forces acting on an object.