FORCES episode II newton strikes back Physics Mr. Maloney

FORCESFORCES episode II episode IInewton strikes newton strikes backback

PhysicsMr. Maloney

© 2002 Mike Maloney

A new era of physicsA new era of physics Aristotle (384-322 BC) thought that objects were

naturally at rest, would always stop themselves and a force was needed for any motion.

Descartes (1596-1650) thought that some unseen vortex was constantly pushing on things to make them stay in motion.

Galileo (1564-1642) realized that the Greeks weren't accounting for forces such as friction.

Newton summarized Galileo's thoughts and others through his three laws of motion.


objectivesobjectives

You will be able todescribe how mass, force and acceleration

are related to eachother.describe the consequences of

Newton’s 2nd Law.graph data to find a relationship between

variables. Jump to Post Lab


Newton’s 2Newton’s 2ndnd Law Law

Newton’s 2nd law describes how a mass behaves when forces act on it.

We can guess these forces will produce a change in motion but how are they related?

ILD 2.2 (1st part)


Newton’s 2Newton’s 2ndnd Law Law

How does acceleration relate to force?Lets do a little experiment together as a

class to find out.

Accelerom eterForce Sensor


Newton’s 2Newton’s 2ndnd Law Law How does this acceleration relate

to the force? The acceleration will be in the same direction

as the force. The magnitude of the acceleration increases

as the force increases The magnitude of the acceleration decreases

as the mass of the object increases Recreate our lab using this sim.


N2L with multiple objectsN2L with multiple objects

What if there is more than one object applying a force on some mass? What is the effect now? (back to ILD)

It is not just one force that determines how an object will change it motion, it is the sum total of all forces acting on the object … what we call NET FORCE.

Demos with 2 fans and 2 weights.


Newton’s 2Newton’s 2ndnd Law Law In mathematical terms

a = F/macceleration = net force / mass

or more commonly writtenForce (net) = mass ∙ accelerationF = m∙a

And since force and acceleration are vectors, they will be in the same direction.


MEASURING FORCESMEASURING FORCESThe unit of force is the Newton {N} It is derived from its effect.F = m*a [kg]*[m/s2]1 N = 1 kg•m/s2 1 N is defined as the amount of force

required to accelerate 1 kg at a rate of 1 m/s2.


22ndnd Law Examples Law Examples

Accelerating a car vs. truckSlowing down a car vs. truckJogging vs. sprintingPushing chair alone vs. someone in itFreefall


objectivesobjectives

Can youdescribe how mass, force and acceleration

are related to eachother.describe the consequences of

Newton’s 2nd Law.graph data to find a relationship between

variables. Jump to Post Lab


APPENDIXAPPENDIX


InertiaInertia

The tendency of an object to resist a change in motion is called its inertia.

Objects with greater masses generally have greater inertias.

For our purposes, an object’s inertia is basically measured by it mass.

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Net ForceNet Force NET FORCE refers to the vector sum total

of all forces acting on an object. It is often expressed as F

For example, if there were two leftward forces of 10 lb each, the NET FORCE would be 20 lb leftward.

If there were one 10 lb rightward force and one 8 lb leftward force, the NET FORCE would be 2 lb rightward.

What about if the forces were in X and Y?

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Applied ForceApplied Force

APPLIED FORCE refers to a generic force that is acting on an object.

An APPLIED FORCE is basically any force that is not a WEIGHT, NORMAL FORCE, FRICTIONAL FORCE, SPRING FORCE, or other named force.

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FORCES episode II newton strikes back Physics Mr. Maloney