FORCESFORCESepisode Iepisode INewton’s hopeNewton’s hope

PhysicsMr. Maloney

ObjectivesObjectives

You will be able to …understand the idea of forcecategorize forces into the two main types

of force recognize when forces existuse Newton’s 3rd Law to describe how

objects interact with each other.

ForcesForces

So far we worked on observing and describing motion

Our next goal will be to figure out what causes motion to change or not change.

How do objects interact?How do objects interact?

Dragging thingsPunching a WallHitting in football or HockeyJumping in dancing or skatingTossing in cheerleadingA push or a pull

What is a Force?What is a Force?

A push or pullForces are the way objects interact.This interaction can cause the objects’

motion to change (acceleration), or it could cause nothing at all depending on the circumstances and how many objects are interacting.

What is a ForceWhat is a Force

Forces are VECTOR quantitiesThey have a magnitude (SIZE) and a

direction

Types of forcesTypes of forces

There are two types of forcesContact ForcesAt a distance forces

Contact ForceContact ForceForces for which the two

interacting objects have to be physically in contact with each other for the forces to exist.

EXAMPLESHittingPulling with a ropeLifting weightsPushing a couchLying on a table

Poking someoneSliding to block a

kickHanging from a

window ledge

Forces in which the two interacting objects are not in physical contact with each other, but are still able to exert a push or pull and interact with each other despite the physical separation.Know any?

At A Distance ForceAt A Distance Force

Examples of ForcesExamples of Forces Contact

Friction Force (Ff, f)

Tension (FT, T)

Normal Force (FN, N)

Air Resistance (Fair)

Applied Force (Fa, F#)

Spring Force (Fsp)

At a Distance Gravitational Force (Fg)

Electrical Force (FE)

Magnetic Force (FM) Nuclear Forces

An Aside …An Aside …4 Fundamental Forces4 Fundamental Forces

We will use a large number of forces, but there are actually only four different kinds of forces in the universe:

1. The gravitational force - how objects with mass interact with one another

2. The electromagnetic force - how charged objects interact with one another (all contact forces can be traced to electromagnetic interactions)

3. The strong nuclear force - holds nuclei together 4. The weak nuclear force - associated with

radioactivity

Newton’s LawsNewton’s Laws In the 1600’s, Isaac Newton established 3

laws of motion which described the relationship between motion and Force.

For this chapter’s project, create a MultiMedia presentation on Isaac Newton’s Laws….

Recreate examples demonstrating his 3 laws of motion and his law of gravity.

Lets See some from other years!

How things interact (How things interact (ILD 2.1))

When you hit a wall with your fist what happens?

When a bug splats on your windshield what happens?

How about when you push a couch across a floor?

How do you interact with these objects … how do they interact with you?

Results of ILD 2.1Results of ILD 2.1

A bug splats on your windsheild as you are driving. What feels a bigger force?

A) The bug does

B) The windshield does

C) They feel the same force

D) Neither feel any force

Newton’s 3Newton’s 3rdrd Law Law For every action there is an equal

and opposite reaction Forces always occur in equal magnitude and

opposite direction pairs. Forces only exist during interactions. One of the pair forces acts on one object, and

the other pair force acts on the other object The 3rd law is often called the law of action-

reaction (even though I don’t like it)

Newton’s 3Newton’s 3rdrd Law Law

Why are people so often tricked. Why do we think the bug feels a greater force than the windshield, when in reality they feel the same?

Although the forces are the same the effect of the force on each object is different. That force on the bug squishes it, but the same force on your windshield only gives you something to clean.

Newtons 3Newtons 3rdrd Law Examples Law ExamplesTake a few minutes and write down how you think

Newton’s 3rd law applies to these situations. Describe what objects are interacting, and what is the effect of these interactions.

You are swimming thru a pool of water Car driving on flat ground A gun shoots a bullet and recoils Punching a wall or paper You jump out a window and fall to the ground Bart and the fire extinguisher

Objectives summaryObjectives summaryDo you…Understand the idea of force

Forces are vector pushes or pulls which have a magnitude and direction

Be able to Categorize forces into the two main types of force

Contact and At a Distance ForcesBe able to Recognize when forces exist

Forces only exist during interactions between objects

Be able to use Newton’s 3rd Law to describe how objects interact.

Forces occur during interactions and are equal in size on each object but opposite in direction.

Newtons 3Newtons 3rdrd Law Examples Law Examples

Identify at least 6 pairs of 3rd Law forces in the situation below …