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# Addition of velocities in the Newtonian physics - PowerPoint PPT Presentation

Addition of velocities in the Newtonian physics. v= speed of the train measured from the platform. w 2 =man’s speed measured from the platform. w 1 =man’s speed measured from the train. w 2 =v+w 1. V. w 1.

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Presentation Transcript

v= speed of the train measured from the platform

w2=man’s speed measured from the platform

w1=man’s speed measured

from the train

w2=v+w1

V

w1

If atorch is switched on on the train, from platform we should measure the speed of light as

w=v+c

where v is the train speed and c is light speed from the train

w>c

V

c

the man on the platform measures the same light speed from the train

so

the Newtonian physics laws are not valid any more

So, we need another rule to add velocities

v+w1

w2=v+w1

w2=

vw1

1+

c2

• In Einstein’s physics:

• c doesn’t depend on the observer

• c is a limit speed,

In 1968 professor Bertozzi used the linear accelerator of the MIT to verify Einstein’s Theories.

Bertozzi used the accelerator to accelerate clusters of electrons. According to the Newtonian physics the speed of electrons should proportionally increase as we add energy without any limit

Instead of following a linear progression the experimental graphic turned out to be like this:

V

Linear prediction

C

Limit speed

Speed of electrons

Light speed

Experimental results

Electrons kinetic energy

Once again Newtonian physics is not valid

Muons are subnuclear particles which are created by interaction of cosmic rays with high atmosphere

Muon average lifetime as measured in laboratory is 2,2x10-6s, we’ll call it t.

After their creation, muons run toward the earth at 0,995 c

Since muons are created at 5000m from earth surface, with a simple

computation we find out that they can’t reach the earth:

0,995c x (2x10-5s)= 657m

But we detect them on the earth!

5000 m

Einstein gives us the answer to this problem.

In Einstein’s physics time is not absolute: every time evaluation must be referred to a specific observer.

Muons lifetime is actually longer than t.

Basing on the value measured in laboratory, we obtain the muon lifetime following this equation

t

t‘=

t‘> t

1-v2/c2

Now, let’s apply Einstein’s theory to the muon problem:

t

t‘=

2.20x 10-6 s

t‘= = 2,20x10-5 s

1-v2/c2

1- (0,995c)2/c2

(0,995c)(2.2x10-5)=6570m

Now muons can reach the earth

5000 m

Anyway, Newtonian physics is still valid and useful in many situations in everyday life.

Relativistic effects are not measurable at everyday speed.

For example, travelling on the Space Shuttle, nowadays the fastest human vehicle, at 28000 km/h:

Time delay per second is

only 0,000000000333 s.

So, a clock positioned on the shuttle will be one second late in 100 years

Supervision: Prof. Barbara Ranco