1. When ready, begin the Slide Show (press F5) on this slide.
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2. Farmer Brown carries a
Ladder (rest length 5 m)
into a
Barn (rest length 4 m)
The relative speed of the Ladder and the Barn is 0.8c

3. Cow’s frame:
A (smart) cow is standing next to the Barn.
Cow measures the Barn to be 4 m.
Cow measures Ladder (which is length contracted) to be 3 m.

4. Farmer Brown’s frame:
Farmer Brown is holding the Back of the Ladder.
Farmer Brown measures the Ladder to be 5 m.
Farmer Brown measures Barn (which is length contracted) to be 2.4 m.

5. Question: Who is correct?
Puzzler: Does the Ladder fit in the Barn?
According to Cow, Ladder is 3 m and Barn is 4 m (can fit)
According to Farmer, Ladder is 5 m and Barn is 2.4 m (can’t fit)
Question: Who is correct?
The Farmer?
The Cow?
Neither the Farmer nor the Cow?
Both the Farmer and the Cow?
Consider the following events --
A: Front of Ladder passes Entrance to Barn
B: Front of Ladder passes Exit to Barn
C: Back of Ladder passes Entrance to Barn
D: Back of Ladder passes Exit to Barn

6. A  C  B  D Cow’s Frame A: Front of Ladder passes Entrance to Barn
C: Back of Ladder passes Entrance to Barn
B: Front of Ladder passes Exit to Barn
D: Back of Ladder passes Exit to Barn
A  C  B  D

7. A  C  B  D Cow’s Frame t (ns)
x (m) 1 2
(10 lt-ns) 5
(20 lt-ns)
t (ns)
10 ns
20 ns 4
Entrance to Barn
Exit to Barn D
D: Back of Ladder passes Exit to Barn
Back of Ladder
v = 0.8c  INVERSE SLOPE of world-line B
B: Front of Ladder passes Exit to Barn
A  C  B  D
Front of Ladder C
C: Back of Ladder passes Entrance to Barn A
A: Front of Ladder passes Entrance to Barn

8. A  B  C  D Farmer’s Frame
A: Front of Ladder passes Entrance to Barn
B: Front of Ladder passes Exit to Barn
C: Back of Ladder passes Entrance to Barn
D: Back of Ladder passes Exit to Barn
A  B  C  D

9. Farmer’s Frame t (ns) x (m) D Back of Ladder Front of Lader1 2
(10 lt-ns) 5
(20 lt-ns)
t (ns)
10 ns
20 ns 4
Back of Ladder
Front of Lader
Farmer’s Frame D
D: Back of Ladder passes Exit to Barn
Exit to Barn C
C: Back of Ladder passes Entrance to Barn
Entrance to Barn A
A: Front of Ladder passes Entrance to Barn B
B: Front of Ladder passes Exit to Barn