PHYSICAL SCIENCE PSC1801Physics in Films

© Christos Velissaris & Costas Efthimiou

LECTURE

Motion, Speed, and Acceleration

• 1,800 Herz• 1,800,000 Herz• 1,800,000,000 Herz• 1,800,000,000,000 Herz• None of the above

REVIEW QUESTIONIf you operate a cell phone, you send and receive waves. A characteristic of the waves is their frequency which is measured in a unit called Herz. If your cell phone operates at 1800 MHerz then it operates at

• 0.000 000 001 meter• 0.000 001 meter• 0.001 meter• 0.1 meter• None of the above

REVIEW QUESTIONModern technology can construct devices that are very small in size. This technology is currently known as nanotechnology. If a device is a 0.001 m, then its size is

• A problem stated and solved by the Italian physicist Enrico Fermi.

• A problem stated by Fermi and solved by Albert Einstein.• Any kind of quantitative question we mind ask and which

we try to answer with rough estimations and yet get a very good answer.

• The calculation of the energy released during an atomic explosion.

• There is no such phrase.

REVIEW QUESTIONWhat does the phrase Fermi Problem mean?

6/22/2015

• International System of Units (SI)• Average & Instantaneous Speed• Average Acceleration• Acceleration of gravity

In physics, there are three basic quantities that are the basis for everything:

Length, Time, Mass

We understand all these quantities from experience but we find very hard to define!

Mass is the quantity of matter in an object. It is also the measure of the inertia that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way.

To compare the inertia, or mass, of two objects, accelerate them side-by-side. The one

that requires the most force is the one with the larger mass.

International System of Units(abbreviated SI from Système Internationale)

Length meter mTime second sMass kilogram Kg

Quantity unit symbol

The meter, second, and kilogram are called base units in SI

Other units are expressed in terms of them

To find a speed requires measurements

of length and time.

average speed = distance/time

v = d/t

Average speed is distance traveleddivided by the time used.

What is the unit of speed in SI?

Speed=length/time

Quantity unit symbol

International System of Units

Length meter mTime second sMass kilogram KgSpeed meter/sec m/s

Quantity unit symbol

What is the average velocity of the sprinter?

distance = 100 m

What is the average velocity of the sprinter?

Distance = 100 m done in about 10 s. Therefore

Average speed = distance / time = (100 m)/(10 s) = 10 m/s

time = 0s time = 10sdistance = 100 m

A sprinter who starts running once the signal is sound. Initially, he has no speed. However, after a second he has a considerable speed. Therefore, his speed changed in a brief amount of time and keeps increasing.

The average speed of the sprinter is not necessarily his actual speed.

The real speed at any moment is called instantaneous speed.

Choose the correct statement:

A. Instantaneous speed is the same as average speed

B. Instantaneous speed and average speed aremeasured in different units

C. Instantaneous speed and average speed aremeasured in the same units.

D. The speedometer of a car shows the average speed.

(final speed – initial speed)acceleration =

time required

Galileo, age 60, drawn by contemporary

Ottavio Leoni in 1624.

Galileo was the first to analyze motion in terms of measurements

and mathematics.

He described acceleration, which is the rate of change of

speed.

Choose the correct unit of acceleration in S.I.

A. m/s

B. m/s2

C. m/s3

D. m/s4

E. None of the above

International System of Units

Length meter mTime second sMass kilogram KgSpeed meter/sec m/s

Quantity unit symbol

Acceleration meter/sec2 m/s2

What is the average acceleration of the sprinter?

final speed = 20 m/s

final time = 10 sinitial speed = 0 m/s

initial time = 0 s

What is the average acceleration of the sprinter?

final speed-initial speedAverage acceleration = = 2 m/s2

time difference

final speed = 20 m/s

final time = 10 sinitial speed = 0 m/s

initial time = 0 s

We are about to see a clip from Speed 2. The clip shows the crashing of a cruise ship into a port. The director has tried to make the scene look very dramatic. We shall compute the deceleration of the ship (as meant by the director) to decide how bad or how realistic the collision is.

Two thumbs up or two thumbs down?

play clipChapter 24: Coming Into Port

time speed in knots speed in m/s deceleration123456789

10.5

9.6

0

10.2

5.3

1.32.0

7.36.9

0

Knots are nautical miles per hour

1 nautical mile = 1.85 Km = 1850 m

1 land mile = 1.6 Km = 1600 m

sm

sm

hmilenauticalknot 514.0

360018501

time speed in knots speed in m/s deceleration123456789

10.5

9.6

0

10.2

5.3

1.32.0

7.36.9

0 5.255.104.803.653.452.651.000.65

0

1 knot = 0.5 m/s

Before any calculation, rate the realism of the crashing of the cruise ship on the port using a scale from 1 to 5. Please rate it according to the appeal the scene has for you.

A. 1: completely unrealistic

B. 2: somewhat unrealistic

C. 3: somewhat realistic

D. 4: very realistic

E. 5: extremely realistic

time speed in knots speed in m/s deceleration123456789

10.5

9.6

0

10.2

5.3

1.32.0

7.36.9

0 5.255.104.803.653.452.651.000.65

0

1 knot = 0.5 m/s

time speed in knots speed in m/s deceleration123456789

10.5

9.6

0

10.2

5.3

1.32.0

7.36.9

5.255.104.803.653.452.651.000.65

0

1 knot = 0.5 m/s

36:59

38:01

39:27

44:05

41:27

38:33

42:13

44:20

43:49

62s32s56s120s46s96s16s15s

0.0024 m/s2

0.0094 m/s2

0.0206 m/s2

0.0017 m/s2

0.0272 m/s2

0.0172 m/s2

0.0219 m/s2

0.0433 m/s2

Want more nonsense? Here is coming…

play clip

Chapter 1: Tango goes trucking