Chapter 7 Motion Applied Lab Physics Mrs. Campbell

Chapter 7Motion

Applied Lab Physics

Mrs. Campbell

Ch. 7, Lesson 1What are Motion and Speed?

• Motion - A change in position.

• Elapsed time - The length of time that passes from one event to another.

• Speed - The rate at which the position of an object changes.

• Distance - The length of the path between two points.

Ch. 7, Lesson 1What are Motion and Speed?, con’t

Example: Calculating Elapsed Time

• Your flight began at 8:00 PM and ended at 11:00 PM. How long did your flight take?

• Elapsed Time = Arrival Time – Departure Time

11:00 PM – 8:00 PM =

• 3 hours

Ch. 7, Lesson 1What are Motion and Speed?, con’t

Practice Problem: Calculating Elapsed Time

• Your flight began at 7:00 PM and ended at 9:00 PM. How long did your flight take?

• Elapsed Time = Arrival Time – Departure Time

• Elapsed Time = 9:00 PM – 7:00 PM

• Elapsed Time = 2 hours

Ch. 7, Lesson 1 What are Motion and Speed?, con’t

Example: Calculating Average Speed• An airplane travels 810 miles in 3 hours. What is the

average speed of the airplane?

• Average speed = Distance Time

• Average speed = 810 miles 3 hours

• Average speed = 270 miles

1 hour• The average speed of the airplane is 270 miles per

hour.


Practice Problem: Calculating Average Speed• An airplane travels 1230 miles in 5 hours. What

is the average speed of the airplane?

• Average speed = Distance Time

• Average speed = 1230 miles 5 hours

• Average speed = 246 miles 1 hour

• The average speed of the airplane is 246 miles per hour.


Calculating Distance – knowing speed and time we can calculate distance with the formula

• Distance = speed x time

• Example – If you can travel 50 miles per hour and you travel for 6 hours, what is the distance traveled?

• Distance = speed x time

• Distance = 50 miles x 6 hours

1 hour

• Distance = 300 miles


Practice Problem - Calculating Distance

• If a car travels 60 kilometers per hour and travels for 7 hours, what is the distance traveled?

• Distance = 60 km x 7 hours

1 hour

• Distance = 420 km


Calculating Time – knowing distance and speed we can calculate the time it will take to travel that distance.

• Time = distancespeed


• Example – Calculating Time

You have a job marking lines on a sports field. The distance to be marked is 80 meters. You mark at the speed of 50 meters per minute. How much time will it take to mark the line?


• Time = 80 meters

50 meters per minute

• Time = 1.6 minutes


• Practice Problem – Calculating Time

A car went 70 miles at an average speed of 60 miles per hour. How long did it take to travel the 70 miles?


• Time = 70 miles

60 miles per hour

• Time = 1.166666 = 1.17 hours

Ch 7, Lesson 2 Using a Graph to Describe Motion

• Constant Speed – Speed that does not change.

• On a graph, constant speed is shown by a straight line.Graph showing constant speed

Distance (km

)

Time (hrs)


• Velocity – the speed and direction in which an object is moving.– Example of Velocity – 200 m in 7 seconds, east.


•Varying Speed – Speed that is not constant.

•On a graph, varying speed will be shown by a non-straight line

Graph showing varying speed

Distance (km

)

Time (hrs)


• Using a Graph to Find Unknown Distances

• We can use a graph for constant speed to find an unknown distance or time.


• Using a Graph to Predict Distances

• We can use a graph for constant speed to predict a distance that is not on the graph.

Ch 7, Lesson 3 Acceleration

• Acceleration – the rate of change in velocity.

Acceleration = Change in velocity

Change in time

Change in velocity = final speed – original speed

Change in time = end time – start time


• Acceleration – Example Problem

A car starts from a stopped position. After 5 seconds, it has a speed of 40 km/hr. What is the car’s acceleration?

Acceleration = Change in velocity

Change in time

Acceleration = 40 km/hr

5 second

Acceleration = 8 km/hr per second


• Deceleration – a form of acceleration used for the rate of slowdown.

• Deceleration is indicated by a negative (-) number or by using the word deceleration.

Ch 7, Lesson 3 Acceleration• Example Problem – A car is traveling at 20 km/hr. The driver suddenly

puts on the brakes. The car comes to a complete stop 4 seconds later. What is the rate of acceleration?

Acceleration = Change in velocity Change in time

Acceleration = 0 km/hr – 20 km/hr 4 sec

Acceleration = -20 km/hr 4 sec

Acceleration = -5 km/hr/sec or the vehicle decelerated at 5 km/hr/sec


• Practice Problem – AccelerationA car starts from a stopped position. After 8 seconds,

the car has a speed of 40 km/hr. What is the car’s acceleration?

• Formula Acceleration = Change in velocity Change in time• A = 40 km/hr – 0 km/hr 8 sec – 0 sec• A = 40 km/hr 8 sec • Acceleration = 5 km/hr/sec

Ch 7, Lesson 4 The Laws of Motion

• Sir Isaac Newton (1643 – 1727) was an English scientist and mathematician.

• He is famous for his discovery of the law of gravity.

• He also discovered 3 laws of motion that we call Newton's Laws of Motion.

• These laws describe the motion of all objects we experience in our everyday lives.


The 1st Law of Motion

•An object at rest tends to stay at rest and an object in motion

tends to stay in motion unless acted upon by an unbalanced

force.


What does this mean?• Basically, an object will “keep doing

what it was doing” unless acted on by an unbalanced force.

• If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving.

• It takes force to change the motion of an object.


• What is meant by unbalanced force?

• If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion.

• If the forces are not equal and opposite, then the forces are unbalanced and the motion of the object changes.


Some examples from real life…

• A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

• Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.


Newton’s First Law is also called the Law of Inertia.

• Inertia: the tendency of an object to resist changes in its state of motion.

• The First Law states that all objects have inertia. The more mass an object has, the more inertia it has (and the harder it is to change its motion).


More Examples from Real Life

• A powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them.

• On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).


• If objects in motion tend to stay in motion, why don’t moving objects keep moving forever?

• Things don’t keep moving forever because there’s almost always an unbalanced force acting upon it.

• A book sliding across a table slows down and stops because of the force of friction.

• If you throw a ball upwards it will eventually slow down and fall because of the force of gravity.


In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever.

Newton’s Second Law

Force equals mass times acceleration.

F = ma

• Acceleration: a measurement of how quickly an object is changing speed.

What does F = ma mean?• Force is directly proportional to mass and

acceleration. Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force.

• Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball.

What does F = ma mean?, con’t

• Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

More about F = maYou double the mass, you double the force. If

you double the acceleration, you double the force.

What if you double the mass and the acceleration?

(2m)(2a) = 4F

Doubling the mass and the acceleration quadruples the force.

So . . . what if you decrease the mass by half? How much force would the object have now?

What does F = ma say?

F = ma basically means that the force of an object comes from its mass and

its acceleration.

• Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.

What does F = ma say? con’t

• Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force.

Newton’s Third Law

For every action there is an equal and opposite reaction.

What does this mean?

• For every force acting on an object, there is an equal force acting in the opposite direction.

• Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving.

• There is a balanced force acting on you– gravity pulling down, your seat pushing up.

Think about it . . .

Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force.

Review• Newton’s First Law: Objects in motion

tend to stay in motion and objects at rest tend to stay at rest unless acted upon by an unbalanced force.

• Newton’s Second Law: Force equals mass times acceleration (F = ma).

• Newton’s Third Law: For every action there is an equal and opposite reaction.

Ch 7, Lesson 5 Gravity

What is a Force?

• FORCE = Any push or pull which causes something to move or change its speed or direction.


GravityGravity: An attraction force between any two objects that have mass.

Newton’s Universal Law of Gravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe.

The amount of gravitational force depends upon the mass of the objects and the distance between the objects.


The greater the mass, the greater the force.force.

The greater the distancedistance, the lessless the force.

Acceleration due to gravity =

9.8 m/s/s or 9.8 m/s2


Weight is a measure of the gravitational force between two objects.

The greater the mass the greater the force (weight).

Measured in units called Newtons (N).


Weightlessness – free from the effects of gravity.


Gravity and Acceleration Gravity causes all objects to have the

same acceleration as they fall. Another force, air resistance also acts on

falling objects.

Air resistance - The force of air exerted on a falling object.

The air pushes up as gravity pulls down.


What is Friction?

Friction = A force that opposes or slows down motion.

Caused by the physical contact between moving surfaces.

The amount of friction depends upon the kinds of surfaces and the force pressing the surfaces together.

Changes motion into heat.

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Chapter 7 Motion Applied Lab Physics Mrs. Campbell