FA Quiz
A fly-by review of forces, inertia, and friction…
THE BIG IDEAS from the last class… A force is a push or a pull A force is measured in Newtons Forces that are equal and opposite in direction are balanced. Unbalanced forces cause changes in motion that can be predicted and described.
Inertia – IS NOT A FORCE tendency to resist any change in motion property of all matter tendency to resist any change in motion object at rest, tends to remain at rest object in motion, will keep moving at the same speed and in the same direction (same velocity)
Inertia greater the mass, the greater the inertia direct or linear relationship to mass greater the mass, the greater the inertia greater the inertia, the larger the force needed to change its velocity
Which has greater mass – a bowling ball or a Ping-Pong ball? Which has more? Which has greater mass – a bowling ball or a Ping-Pong ball?
2. Which has more inertia– a bowling ball or a Ping-Pong ball?
Which has more? 3. Which will require more force to change its motion – a bowling ball or a Ping-Pong ball?
A force that opposes motion between two surfaces that are in contact Friction A force that opposes motion between two surfaces that are in contact
Direction of Friction Friction always points in the direction that resists motion FRICTION
Two main types of friction Static friction – occurs when a force is applied to an object but does not cause motion Kinetic friction – Friction between moving surfaces
Three Kinds of Kinetic Friction Sliding Friction – When solid surfaces slide over each other Rolling Friction – When an object rolls over a surface Fluid Friction – When an object moves through a fluid
How to Increase/Decrease Friction Greater forces applied to the object increase friction
How to Increase/Decrease Friction Rougher surfaces on the objects increases friction VS.
How to Increase/Decrease Friction The amount of area in contact does not affect friction
Air Resistance Air resistance is a force that slow down objects that are moving through the air. Air resistance is caused by the collision of a solid object with gas molecules in the atmosphere. The greater the surface area of the object, the greater air resistance The shape of the object also determine how much air resistance is present The faster an object is falling through air (its speed), the greater the air resistance
Friction – Helpful or Harmful?
How do Wheels reduce friction Textbook Plastic grocery bag Spring scale Rubber band Pencils Marbles Directions Put your textbook in a plastic grocery bag. Hook the spring scale to the handles and pull the book across the table. Read the measurement on the spring scale while the book is at a constant motion. Record the measurement on the chart. Be sure to label all units. Repeat steps 1-4 using the pencils and the marbles. Put a rubber band around the book & the plastic grocery bag and repeat steps 1-4. Data Table Surface Force Book in a bag Book on pencils Book on marbles Book with rubber band
Discuss Results What is friction? Which object acts like wheels? Explain why. In which example was the force of friction the least? Explain. In which example was the force of friction the greatest? Explain. List four ways friction is helpful in your life.