Forces, Gravity, and Friction

​Science Root of the Day:

DO NOW: Write what you think the example words mean in your lab manual.

Extra Credit: Find three additional words that use this root and write them and their definition in your lab manual (6 Points Max)

Unit 7 Section 2-Forces, Friction & Gravity

Multiple Choice

The rate at which an object's Velocity changes is the object's

• Speed

• Distance

• Acceleration

• Direction

Multiple Choice

Which of the following is the SI unit of acceleration?

• m/s

• m/s²

• m²/s

• s/m²

Multiple Choice

Which of these is an example of deceleration?

• a bird taking off for flight

• a roller coaster moving down a steep hill

• a safe driver approaching a red light

• an airplane following a straight flight path

• Describe what a force is

• Compare Balanced to Unbalanced forces

• Describe how forces relate to the motion of an object

• Describe friction and gravity

  • Compare and contrast how the two affect motion

​Lesson Objectives

How are Forces Described?

• Force: A push or A pull on an object

  • Can act on or between two objects both in direct contact and not touching

• Force has a magnitude and a direction

  • Magnitude=strength

  • Direction is indicated with an arrow

• Measured using the unit of Newtons

How do Forces Affect Motion?

• Often multiple forces act on an object at one time

• Net Force: The Combination of all Forces on an object

  • Found by adding all the forces acting on the object together

  • Has a direction indicated by an arrow

  • Has a magnitude indicated by a number

• When the Net Force is Zero, an object is still

• An unbalanced, non-zero force changes an object's speed or direction

  • Moves in the direction of the larger force

Calculating Net Force

• What is the net force in this picture

  • Add the two Force Values together

Fill in the Blank

What is the Net Force?

Calculating Net Force

• What is the net force in this picture?

  • In this question, the two dogs are going in opposite directions

  • We Think of the going to the right as positive and going to the left as negative

  • Force= 20 + -10

Fill in the Blank

What is the Net Force?

Multiple Choice

What is the net force?

• 5.5 N left

• 5.5 N right

• 2.5 N left

• 2.5 N right

Multiple Choice

What is a force?

• the PUSH or PULL on an object 

• The MOTION an object creates

• The objects HITTING one another

• Going REALLY FAST

Multiple Choice

If these boys are pulling with the same amount of force.  What will happen?

• The boy in blue will win.

• They will not move at all.

• The boy in red will win.

• Both will fall down.

Multiple Choice

What is the net force?

• 11 N left

• 11 N right

• 3 N left

• 3 N right

Multiple Choice

With unbalanced forces, the object will move in the direction of the _______ force.

• larger 

• smaller 

• equal 

What is Friction?

• Friction: A force that two surfaces exert on each other when they rub against each other

  • From the Latin word fricare- to rub

  • Acts opposite the force of motion

    • Is the force that eventually stops an object from moving

What Factors affect Friction?

• There are two factors that affect how the force of friction works

  • The type of surfaces involved

    • A smoother surface has less friction than a rough one

What Factors affect Friction?

• There are two factors that affect how the force of friction works

  • How hard the surfaces are pushed together

    • A heavier object experiences more friction because it is pushing harder against the ground

Different Types of Friction

• Whenever two objects physically interact, there is some form of friction

• There are 4 different types of friction

  • Sliding Friction

  • Static Friction

  • Fluid Friction

  • Rolling Friction

Sliding Friction:

• Occurs when two solid objects slide across each other

• Makes objects slow down and stop

Static Friction:

• Acts between two solid objects that are not moving

• A force that stops movement from happening

  • Think about moving a heavy couch.

    • You need to push very hard to move it

Fluid Friction

• Occurs when a solid object moves through a fluid material

  • Liquid or air

• Is easier to overcome than sliding friction

Rolling Friction

• Occurs when an object rolls across a surface

• Is much easier to overcome than sliding friction

  • Only a small portion of the object is in contact at any given time

Match

Match the following Types of Friction to their descriptions

• Static Friction

• Slide Friction

• Fluid Friction

• Rolling Friction

Pushing a stationary car

Sledding down a hill

A plane flying through the air

A skateboarder going down a ramp

• Pushing a stationary car

• Sledding down a hill

• A plane flying through the air

• A skateboarder going down a ramp

Multiple Choice

When does Friction Occur?

• When an object Falls

• When two objects collide

• When two objects are close by each other

• When two objects rub together

What is Gravity?

• Gravity: A force that can act at a distance to pull objects toward each other

  • First Discovered by Sir Isaac Newton in ~1665

    • Watched apples falling from trees and wondered why they fall downward instead of to the side or upwards

• Gravity is the force that pulls objects to the Earth and makes them fall

Universal Gravity

• Newton realized that gravity acts all around us, not just on the Earth

  • Including Space

• The Law of Universal Gravitation: The force of Gravity acts between all objects that have mass

  • Anything that has mass feels a pull towards the objects with mass around them

  • Keeps the Planets in Orbit

If objects with Mass are attracted to one another, why do they not fly off into space toward each other? 

Factors Affecting Gravity

• The Gravitational force between some objects is stronger than the force between others

• There are two factors that affect how Gravity acts on objects: Mass and Distance

  • Mass: The larger an object is, the larger its pull on other objects

  • Distance: The farther apart two objects are, the weaker they pull on each other

Ocean Tides & Gravity

• ​The tides are connected to the moon through the force of Gravity

• As the moon revolves around the Earth, the force of Gravity changes depending on which side of the Earth it is on​

Weight vs. Mass

• Mass and Weight are not the same things

  • Mass Measures how much matter is in an object.

  • Weight measures how much force gravity exerts on an object

    • weight can vary based on where you are in the universe, depending on the gravitational pull in a certain place

Multiple Choice

The force of gravity on a person or object on the surface of a planet is called

• mass.

• weight

• Terminal Velocity

• free fall.

Dropdown

 The force of gravity on a person or object on the surface of a planet is called ​

Select answer