Civil Engineering
What are the two main forces acting on a bridge when weight is placed on it?
Compression (squeezing, at the top) and tension (stretching, at the bottom).
What supplies the energy that launches a projectile from your catapult?
Rubber bands — they store elastic potential energy when stretched, then release it as kinetic energy on launch.
What are the three forces that try to knock a tower down during an earthquake?
Gravity (pulls down), Shear (slides floors sideways), and Overturning (tips the tower from the base).
What two forces are competing every time a parachute falls through the air?
Gravity (pulling down) and drag (air resistance pushing up). The parachute works by maximizing drag to balance gravity.
What shape did engineers discover is the strongest for resisting forces — and can be found in most real bridges?
The triangle. It cannot change shape when pushed, unlike a square which collapses into a parallelogram.
If you want your catapult to launch farther, should you increase or decrease the launch angle from flat ground?
Increase the angle — up to 45 degrees gives the maximum range. Below 45 = too flat; above 45 = too vertical.
What is a 'soft story failure' and why is it dangerous?
When one floor is weaker than the others (like an open parking garage), it collapses first and the whole building pancakes down on top of it.
What is terminal velocity?
The point where drag equals gravity — the parachute stops speeding up and falls at a steady, constant speed.
Name the three main types of bridges and one real-world example of each.
Beam bridge (simple slab), Truss bridge (railroad bridges, old iron bridges), Suspension bridge (Golden Gate, Brooklyn Bridge).
What is the difference between potential energy and kinetic energy?
Potential energy is stored energy (rubber band pulled back). Kinetic energy is energy in motion (the projectile flying through the air).
Why did teams that used marshmallow joints often outperform teams that taped everything stiff?
Flexible joints absorb seismic energy instead of resisting it rigidly. Real buildings use dampers and isolation pads for the same reason — flexibility beats rigidity.
Why does a small vent hole at the top of a parachute actually make it work better, not worse?
It lets a small amount of air escape in a controlled way, which stabilizes the canopy and prevents it from collapsing. Without it, air can rush in from the sides and collapse the whole canopy.
If a bridge fails by bending down in the middle, what is the failure mode called and what should you change?
Sagging or bending. Fix: increase the depth/height of the beam, or add supports underneath. More depth = more resistance to bending.
What type of engineer would design a real launching mechanism — like a rocket or a trebuchet?
A mechanical engineer designs machines and mechanisms, including any system that converts stored energy into motion.
Explain how a tuned mass damper works and name a real building that uses one.
A heavy pendulum or ball inside the building swings opposite to the building's sway, canceling out the vibration. Taipei 101 has a 660-ton damper.
Name three things that affect how fast or slow a parachute falls.
Canopy size, canopy shape, string length, payload weight, and whether there's a vent hole — any three of those count.
Why does the Golden Gate Bridge sway up to 27 feet side-to-side — and why is that a good thing?
Flexibility lets it absorb wind and seismic forces without cracking. A completely rigid bridge would snap under those forces instead.
Why does adding more rubber bands not always make your catapult launch farther?
Too much force can overpower the arm structure and cause it to break or flex instead of transferring energy cleanly. Also, the arm speed may exceed the optimal release point.
What is base isolation and how is it different from X-bracing?
Base isolation sits the building on flexible rubber pads so ground motion doesn't fully reach the structure. X-bracing uses diagonal triangles inside the frame to resist shear forces. One isolates from the ground; the other strengthens the frame.
Why did teams with bigger canopies not always win the parachute challenge?
Canopy size is just one variable. String length, attachment symmetry, shape (dome vs flat), and payload balance all matter. An unstable or collapsed canopy drops fast no matter how big it is.