Introduction Who is the audience? 8 th grade Physical Science Objective This project will allow...

IntroductionIntroduction

Who is the audience?Who is the audience?88thth grade Physical Science grade Physical Science

ObjectiveObjectiveThis project will allow students to learn to solve logic This project will allow students to learn to solve logic and mathematical problems involving motion and forces and mathematical problems involving motion and forces

in an electronic environment.in an electronic environment.

Motion and ForcesMotion and Forces

MotionMotion is defined as the change in position of an object. is defined as the change in position of an object.

Question:Question: If an object is observed to be in the same position two distinctly different times, do you know enough to determine whether it was in motion at any point during this time?

YES

NO


MotionMotion is defined as the change in position of an object. is defined as the change in position of an object.

Question:Question: If an object is observed to be in If an object is observed to be in the same position two distinctly the same position two distinctly different times, do you know different times, do you know enough to determine whether it enough to determine whether it was in motion at any point during was in motion at any point during this time?this time?

Incorrect!Incorrect!

Motion and ForcesMotion and ForcesMotionMotion is defined as the change in position of an object. is defined as the change in position of an object.

Question:: If an object is observed to be in the same position two distinctly different times, do you know enough to determine whether it was in motion at any point during this time?

Correct!Correct!


Motion is measured through the quantities of Speed, Velocity, and Acceleration.

Motion and ForcesMotion and ForcesSpeedSpeed

measurement of how fast position changes. The units of measurement for Speed are meters per second, or m/s. Speed is a scalar quantity, or a quantity with just magnitude or size.

VelocityVelocity

measurement of how fast position changes in a specific direction. The units of measurement for velocity are meters per second East, North, up, down, left, etc., or m/s East. Also, direction can be noted with the use of an arrow ( ). Velocity is a vector quantity, a quantity with both magnitude and direction.

AccelerationAccelerationmeasurement of how fast velocity changes. The unit of measurement for acceleration is the meter per second per second, or m/s2. Acceleration is also a vector quantity though not represented by an arrow or direction per se, rather as a positive (+) or negative (-) acceleration.

Motion and ForcesMotion and ForcesMathematically, speed is the quotient of distance over time, or

S = d/t

In the animation below, the “mouse-surfer” travels an approximate distance of 23 centimeters in five seconds. So, applying the formula above we determine the surfer to have a speed of 4.6 cm/s.

S = d/t = 23 cm/5 s = 4.6 cm/s

23 centimeters


Solve:A wheelchair racer completes a 100-meter course in twenty seconds. What is her speed?

a)5 m/sa)5 m/sb)10 m/sb)10 m/sc)15 m/sc)15 m/sd)20 m/sd)20 m/s



Correct!Correct!

Motion and ForcesMotion and ForcesMathematically, velocity is similar to speed. However, you must denote the

direction of travel for the object in question

v = d/tv = d/t, ,

In the animation below, the “mouse-surfer” travels an approximate distance of 23 centimeters in five seconds. So, applying the formula above we determine the surfer to have a speed of 4.6 cm/s . The length of the arrow is proportional to the magnitude of the velocity. A greater velocity would result in a larger arrow, a lesser velocity would result in a smaller arrow.

23 centimeters


Solve:A wheelchair racer travelling North completes a 100-meter course in twenty seconds. What is her speed?

a)5 m/sa)5 m/sb)5 m/s, Eastb)5 m/s, Eastc)5 m/s, Southc)5 m/s, Southd)5 m/s, Northd)5 m/s, North



Correct!Correct!

Motion and ForcesMotion and ForcesMathematically, acceleration is the quotient of the change in velocity and the

change in time.

a = ∆v / ∆t

= (vf – vi) / (tf – ti) = (final velocity – initial velocity)/(final time – initial time)

A change in velocity denotes a change in speed, a change in direction, or a change in both speed and direction.

For instance, a car accelerating from rest to 15 m/s over five seconds is an example of an accelerating object. Also, a car maintaining a constant speed, say 5 m/s, while driving around a circular track is also an example of an accelerating object. Finally, a car reducing speed while rounding a corner and increasing speed out of the corner is also an example of an accelerating object.


Solve: Solve: A cheetah can go from 0 m/s, rest, to A cheetah can go from 0 m/s, rest, to 20 m/s in 2 seconds. What is 20 m/s in 2 seconds. What is

the the cheetah’s acceleration?cheetah’s acceleration?

a)- 10 m/sa)- 10 m/s22

b)10 m/sb)10 m/s22

c)- 40 m/sc)- 40 m/s22

d) 40 m/sd) 40 m/s22




Correct!Correct!

Motion and ForcesMotion and ForcesA force is simply a push or a pull. Forces cause a change in motion.

The unit of measurement for force is the Newton (N).

One Newton of force causes a 1-kg mass to accelerate 1 m/s2.

1 N = 1 (kg1 N = 1 (kg..m)/sm)/s22

Additionally, forces are vectors, which means they have magnitude and direction. The size of the vector is proportional to the magnitude of the force.

Forces include such physical quantities as magnetism, electricity, gravity, friction, lift, and thrust.


Question:Question: An object is observed to be at rest. An object is observed to be at rest. Moments later the object is observed Moments later the object is observed

to be to be moving away from you, the observer. moving away from you, the observer. Has Has there been a force applied to the there been a force applied to the object to object to cause its motion?cause its motion?

Yes

No




Correct! If an object is in motion it has

been acted on by a force.

Motion and ForcesMotion and ForcesWhen a force is applied to a mass, the motion of the mass has

changed.

Newton’s 1st Law: An object in straight-line motion, or at rest, will remain in straight-line, or at rest, until acted upon by unbalanced outside forces.

Inertia is another way of stating Newton’s 1st Law. The inertia of an object is the object’s resistance to a change in motion. Inertia is strictly dependent on the mass of the object.

The more massive an object, the more difficult that object is to move. Therefore, the object has

more inertia than a lighter object and will require a greater force to change its motion.


Question: Which has more inertia, a 747 jumbo-jet at rest before taxiing to the runway, or a motorcycle travelling 44 meters per second.

Jumbo-jet

Motorcycle


Correct!Correct!

A jumbo-jet has more mass than a

motorcycle, therefore more

inertia. The speed of the motorcycle is not important until

we discuss momentum

Motion and ForcesMotion and ForcesForce and mass determine acceleration.

Newton’s 2nd Law: The acceleration of an object increases with increased force and decreases with increased mass.

FF = maa


Question: According to Newton’s 2nd Law, in order to increase the acceleration of an object you must

Increase force on the object, or decrease mass of object

Decrease force on the object, or increase mass of object



Incorrect!

Increased mass of the object or

decreased force by the person would

result in an unfortunate

circumstance.



Correct!

Increased force by the person or decreased mass of the object would yield good results. The rock moves and the person remains alive

Motion and ForcesMotion and ForcesForces act in pairs.

Newton’s 3Newton’s 3rdrd Law: Law: When one object exerts a force on another object, the second object exerts a force equal in magnitude and opposite in direction on the first object.

ActionAction ++ ReactionReaction

Interaction


Question: According to Newton’s 3According to Newton’s 3rdrd Law, an action Law, an action

force and its force and its reaction force arereaction force are

Equal in magnitude and opposite in direction

Equal in size and direction




IncorrectIncorrect!!


The action-reaction pairsare equal in size and oppositein direction. The two yellow vectors are equal in magnitudeto the red arrow, but opposite in direction. Otherwise, the jack would accelerate throughthe car, or the car would come crashing down on the mechanic.

Correct!Correct!




You’ve completed

your lesson on motion and

forces. Congratulations on a job well-

done!

Created by Rich Edelen, March 2009 Michigan State University

Masters Certificate in Educational Technology

Introduction Who is the audience? 8 th grade Physical Science Objective This project will allow...

Documents

Transcript of Introduction Who is the audience? 8 th grade Physical Science Objective This project will allow...