Motion & Newton’s Laws

Earth Systems

Definition and Formulas

SPEED: a measurement of distance traveled in a given time. Speed = distance

timeUnits: m , mi , km

sec hr hr

Distance: s x t Time: d s

D

S T

Velocity

VELOCITY: an objects speed and direction.Units: m sec North

Graphing

If Sally got to school on foot and bus describe her movement according to the graph.

1: Sally at a slow constant speed walking to the busstop at 0.1 km/min

2: She stopped and sat waiting for the bus 0 km/min

3: She rode the bus at a faster constant speed of 0.25 km/min

Car A Car B Car C

1.Compare the motion of Car A an B.

2.Describe the motion of Car C.

ACCELERATION: Change in velocity

Increase in velocity: acceleration Decrease in velocity: deceleration or negative acceleration.

Acceleration: final velocity – initial velocity time

Units: m sec2

Acceleration equation rearranged for different variables

Unknown: Vi Vi = Vf - (a x t)

Acceleration “dot diagram” Dot represents an object’s position at different times.

Acceleration: distance increases each second

1 sec

1 sec

5 sec3 sec

7 sec5 sec3 sec

Negative Acceleration / deceleration: distance decreases each second

7 sec

Video: Speed, Velocity, Acceleration, and DecelerationA Segment of: Basics of Physics: Exploring the Laws of Motion

Graphing simulation

http://phet.colorado.edu/en/simulation/moving-man

Straight line versus curved line

What is the speed traveled between 0-1sec?

10m/1s= 10 m/s What is the speed traveled

between 4-5 sec? 10m/1s= 10 m/s CONSTANT SPEED

What is the speed traveled between 0-1 sec?

2 m/1sec = 2 m/sec What is the speed traveled between 4-5 sec? 18 m/ 1 s = 18 m/sec CHANGING SPEED, ACCELERATION

Constant speed or acceleration?

Constant speed Acceleration

A force is…a push or a pull.

Friction, Drag, Gravity, and Weight are forces.

Measured in unit Newton’s

N = kg × m

sec2

Calvin explains Newton’s Laws

Sir Isaac Newton is famous for explaining the motion of objects using mathematics.

1st Law: The Law of Inertia

An object in motion will stay in motion, An object at rest will stay at rest, unless an outside force acts on it.

Newton’s 1st Law rap http://www.youtube.com/watch?v=OaKc4PlrEY8

Example: Table cloth trick Penny in a flask

1st law stated again

If no unbalanced force acts on an object the object will continue moving at the same speed in the same direction

If an object is not moving and at rest the object will remain at rest until an outside force acts upon it.

Friction and gravity are the unbalanced forces that are acting on all the motion that we observe.

Friction is the force that slows things down when two objects rub together.

Friction slows objects until they stop, heats things up and wears them down.

Gravity is the force pulling two objects together

Newton’s 1st Law and You

Don’t let this be you. Wear seat belts.

Because of inertia, objects (including you) resist changes in their motion. When the car going 80 m/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

Inertia related to Mass

Bigger masses have more…

Smaller masses have less inertia.

Inertia = Resistance to…

changing speed.

changing direction.

Inertia = resistance to changes in motion.

Large masses resist net forces

and do not accelerate as

easily as small masses.

A large mass resists changing its velocity.

What if we put rockets on each creature?

Large masses resist changing motion.

Small masses change motion easily.

http://videos.howstuffworks.com/discovery/29421-assignment-discovery-newtons-laws-of-motion-video.htm Assignment Discovery: Isaac Newton’s

Principia Exploring the laws of motion: Newton’s

1st law Lego video:

http://www.youtube.com/watch?v=NWE_aGqfUDs

2nd Law

Force = mass x acceleration

Animations: \http://videos.howstuffworks.com/discovery/29421-assignment-discovery-newtons-laws-of-motion-video.htm

http://www.youtube.com/watch?v=7_fbH-muvlw&feature=related “Three laws of motion” Assignment Discovery: Newton’s Laws of Motion (

http://videos.howstuffworks.com/discovery/29421-assignment-discovery-newtons-laws-of-motion-video.htm) show for 2nd law

Force

mass acceleration

2nd Law

Newton = kg x m sec2

One Newton is equal to the force required to accelerate one kilogram of mass at one meter/second every second.

2nd Law (F = m x a) How much force is needed to

accelerate a 1400 kilogram car 2 meters per second/per second?

Write the formula F = m x a Fill in given numbers and units F = 1400 kg x 2 meters per

second/second Solve for the unknown 2800 kg meters/second2 or 2800 N

3rd Law

For every action, there is an equal and opposite reaction.

3rd Law Whenever objects A and B interact with each other, they exert forces upon each other.

When you sit in your chair, your body exerts a downward force on the chair

• The chair exerts an upward force on your body.

ACTION

REACTION

Newton’s 3rd Law in Nature Consider the propulsion of a fish through the

water.

action

Reaction

ACTION FORCE: A fish uses its fins to push water backwards.

REACTION FORCE: the water reacts by pushing the fish forward

3rd Law

Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

MOMENTUM

Momentum = Mass x Velocity

Law of conservation of momentum: If one object loses momentum, the other object gains momentum.

Units of momentum: kg x m sec

Mass Velocity

Momentum

Motion quiz

Motion quiz followed by Newton’s Second Law penny lab

How could you increase the momentum of car E equal to the momentum of car A?

Gravity: force of attraction between all objects in the universe

Universal law of Gravitation

F = G m1m2

d2

F: force of gravityG: constant of universal gravitation 6.67 x 10-11 N∙m2

kg2

m1: mass of object one

m2: mass of object twod2: distance between objects squared

F = G m1m2

d2

Use the universal law of gravitation to compare the force of gravity between

1. Earth & elephant2. Earth & mouse3. Elephant & mouse

Effect of mass and distance

Gravitational force increases as mass increases Example: Gravitational force between elephant

and Earth more then mouse and Earth. Gravitational force decreases as distance

increases.

Misconception: There is no force of gravity in outer space. Yes there is. But the amount of gravity depends on the 2 objects mass and the distance between the two objects.

Universal law of gravitation problems

Constant acceleration of free falling objects

y = ½ g t 2

y = vertical distance traveled

g = acceleration due to gravity (10m/s2 )(rounded from 9.8 m/sec2)

t = time

If a rock is falling off a canyon wall and falls for 20 seconds how far down has it fallen?

y = ½ g t 2

Y= ½ x 10m/sec2 x (20sec)2

Y = ½ x 10m/sec2 x 400 sec2

Y = 2000 meters

Watch video

http://videos.howstuffworks.com/science/falling-object-videos-playlist.htm#video-29420

http://videos.howstuffworks.com/science/gravity-videos-playlist.htm?page=2#video-29423 Issac Newton describing gravity and orbit

http://videos.howstuffworks.com/science/gravity-videos-playlist.htm?page=2#video-29600 2nd explanation of Newton’s description of gravity

Feather vs hammer: http://www.youtube.com/watch?v=KDp1tiUsZw8&safety_mode=true&persist_safety_mode=1

vomit comet: http://www.youtube.com/watch?v=2V9h42yspbo

Acceleration due to gravity.

Objects pick up speed at the same rate regardless of mass when gravity is the only force

The force of gravity is greater on more massive objects but the inertia (resistance to motion) is greater too. For this reason a shot-put and softball will accelerate at the same rate.

Acceleration due to gravity 10 m/sec2

Light objects are affected by frictional forces more then heavy objects.

Terminal Velocity

Falling objects will reach a maximum speed when the upward force of air resistance balances the downward force of gravity.

For humans: 190 km/hr, 120 mi/hr http://www.youtube.com/watch?v=ur40

O6nQHsw&feature=related&safety_mode=true&persist_safety_mode=1 Physics of sky diving 3 min

falling in orbit: http://www.nasa.gov/mov/194279main_044_astronauts_float_in_space.mov

http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Why_Do_Astronauts_Float.html

Objects in orbit like the space shuttle

The space shuttle is moving forward and in free fall toward the Earth.

This results in a curving motion known as orbiting.

Not done 2012-2013REACTION TIME ACTIVITY:

1. On a 7cm x 28cm poster board strip make a short line by one edge near the bottom of the strip label it 0

Calculate the distance an object will fall every .05 seconds

Formula to use: y = ½ g t 2

y: distance g: acceleration due to gravity

10 m/sec2 In centimeters 1000 cm/sec2

Time: calculate for .05 seconds .06 seconds .07 seconds Keep going until 0.22 seconds

1. Mark the falling distances that you have calculated along the edge of the poster board. Next to each mark write the falling time for which it was calculated. Be sure and measure from your zero mark each time.

QUESTION: Why does the distance increase even though the time interval is the same?

QUESTION: why does the distance increase even though the time interval is the same?

The falling object speeds up during each second it is falling – during each succeeding second the object is falling faster and therefore further than during each previous second.

Measure reaction times The person conducting the test holds the

test strip by the top end. The testee holds his/her thumb and

forefinger about 1 cm apart just below the zero mark. (Have the testee rest the catching arm on a table to ensure that he/she does not move the hand down to catch the strip.

The tester lets go of the strip, and the testee snaps his/her fingers shut to catch it.

Record 20 trials. Graph your learning curve as trial # vs.

reaction time.