Can an inch of water really move a car? At first glance, it seems unlikely that such a small amount of water could generate enough force to push a heavy vehicle. However, the physics behind flowing water can create deceptively powerful forces. In flood situations, as little as 6 inches of moving water can be enough to sweep away a person and 12 inches is enough to carry away most cars. But how exactly can a seemingly insignificant depth of water create such a strong effect? There are a few key factors at play.
Quick Answers
– Yes, under certain conditions, as little as 1 inch of moving water can generate sufficient force to move most vehicles.
– The physics of flowing water can create powerful forces – water weighs over 60 lbs per cubic foot and gains momentum as it moves.
– A depth of 6 inches of fast moving water can knock a person off their feet. 12 inches can carry away most cars.
– As a general rule, it’s best to avoid driving through flooded roads, even with seemingly shallow water depths.
The Physics of Moving Water
While water may seem innocuous when sitting still, once it gets moving it gains immense power through its weight, speed, and momentum. To understand how this works, we need to dive into some key physics principles.
Weight
Water is heavy – about 62.4 pounds per cubic foot to be exact. When you multiply that weight across a volume of moving water, it adds up to a hefty force. Even just a 1 inch depth across a 4 foot by 6 foot section of road amounts to about 248 gallons weighing over 1500 pounds.
Speed
Moving water picks up tremendous speed very quickly. As little as 6 inches of water flowing at just 3-4 mph exerts the equivalent force per unit area as air blowing at EF5 tornado wind speeds! Water moving at this speed can easily sweep objects and people off their feet. And the faster it moves, the more power it carries.
Momentum
Finally, moving water builds immense momentum, which gives it incredible power. Momentum is based on mass x velocity. So heavy, fast moving water develops huge momentum that can exert unbelievable force on any object in its path. This allows moving water to push, lift, and sweep away things like rocks, trees, vehicles, and buildings.
Quick Answers
– Water weighs 62.4 lbs per cubic foot. Even 1 inch on a road is over 1500 lbs.
– 6 inches of water moving at 3-4 mph has force like an EF5 tornado.
– Fast moving water builds huge momentum that exerts force on objects.
– Weight, speed, and momentum give moving water incredible power.
Real World Demonstrations
These physics principles play out dramatically in real world flooding events. There are numerous examples that illustrate just how easily moving water can push vehicles around.
Toy Cars in Water Flow
One simple demonstration is to place small toy cars in a straight channel of flowing water. Even with water moving at low speeds, you’ll see the toys easily swept away and tumbling in the current. This small scale setup shows how readily the force of the water overpowers the little cars.
Full Size Cars and Trucks
When you scale up to real full sized vehicles, the water’s power is even more impressive. There are many videos online of cars being picked up and moved by flash flooding. One compilation shows sedans, SUVs, and even a school bus being shoved around residential streets by water that was likely less than 1 foot deep originally.
Automakers’ Demonstrations
Major automakers have filmed demonstrations showing how easily their own vehicles can be moved and lifted by flowing water. Toyota made a video pushing a Prius sideways with an inch of water moving at just 2-3 mph. Honda also has footage of a Civic being carried away in a wet testing pool by less than 6 inches of water.
Quick Answers
– Toy cars in small water channels are easily swept away, showing water’s power.
– Real life videos reveal cars moved by less than 1 foot of water.
– Automakers demonstrate their vehicles drifting easily in shallow water.
– These examples visualize the intense forces water can generate.
The Dangers of Moving Water
It’s clear that rapidly flowing shallow water poses serious dangers that every driver should take seriously. Authorities like the National Weather Service have done extensive research on the risks of vehicles encounters flooded roads.
CDC Statistics
The Centers for Disease Control compiled telling statistics that highlight the hazards of moving water:
– 76% of flood-related drownings occur with vehicles.
– Vehicles can be easily carried away by just 2 feet of moving water.
– It takes just 6 inches of fast moving water to knock over an adult.
– Half of all flash flood deaths happen at water depths less than 2 feet.
Rollover Risk
One of the biggest dangers with water on roads is loss of traction and hydroplaning. Vehicles can start to float and drift even with just 6 inches of water according to AAA. This also greatly raises the chance of the vehicle rolling over, especially with higher profile vehicles like SUVs.
Invisible Threats
Flooded roads also hide hazards below the surface that can trap vehicles. There may be deep scour holes, sharp objects, or erosion under the water. Hitting these unseen threats can mean disaster for any drivers who venture in.
Stranded Motorists
Many flood deaths occur when people become stranded or trapped in stalled vehicles and drown as water levels continue to rise. It only takes 2 feet of water to float many cars, leaving occupants helpless. Attempting to evacuate through deeper, faster moving water poses extreme risks as well.
Quick Answers
– 76% of drownings in floods involve vehicles. Just 2 feet of water can float cars.
– 6 inches of moving water can knock down people and cause cars to hydroplane.
– Unseen hazards under water can trap vehicles and endanger occupants.
– Rapidly rising water leaves people stranded and likely to drown in vehicles.
Avoid Driving in Any Floodwaters
Given the immense power and serious dangers posed by moving water over roads, it is always safest to avoid driving through flooded areas, regardless of how shallow the water appears. A general rule of thumb is that if you can’t clearly see the pavement underneath, you should not attempt to drive through the water.
Turn Around, Don’t Drown
The National Weather Service has popularized the phrase “Turn Around, Don’t Drown” to emphasize that no amount of inconvenience is worth the risk of entering floodwaters. Their guidelines state that roads covered with water should always be considered closed to vehicular traffic.
Wait for Receded or Proper Authorities
Patience is required in flooding events. Never try to cross until water has receded for some time and the roadway can be assessed for damage. Barricades put up by authorities should always be obeyed. Some areas may require professionally equipped rescue vehicles to safely navigate submerged roads.
Trust Your Eyes, Not the Roadway
Even asphalt or concrete below the water can be undermined or deeply scoured out by strong flows. So drivers should rely on visual evidence rather than assuming roads are intact. If water levels look questionable, stay safely clear.
Quick Answers
– It’s always safest to avoid driving through any flooded roads, no matter how shallow.
– The rule is simple – if you can’t see the road, don’t try to drive through it.
– Never go around barriers or disobey warnings from officials.
– Looks can be deceiving – trust your eyes over assumptions about the road.
The Only Safe Choice is to Stay Dry
Ultimately, the incredibly deceptive power of moving water leaves smart drivers with only one choice – stay out of the water entirely. A few inches might not seem like much, but the physics involved means flooded roads can rapidly become deadly. No trip or appointment is worth the risk of being swept away or stranded by floodwaters. The next time you come across a flooded roadway, remember the question isn’t “Can my vehicle make it through?” but rather “Can even an inch of water move a car?” In such a situation, discretion is certainly the better part of valor. So do the safe thing and find an alternate route. The only sure way to arrive safely is to stay dry.
Conclusion
While an inch or two of water may seem harmless at first glance, its physics reveal tremendous power. Through its sheer weight and ability to gain tremendous speed and momentum, shallow but moving water can easily sweep away people, cars, and trucks. Real world examples and tests show that vehicles can be pushed around and lift off the road with amazingly little depths. And floodwaters pose myriad dangers from hydroplaning to hidden road hazards. With the high percentage of flood deaths involving vehicles, it is always safest to turn around and avoid driving through flooded roads, no matter how passable they may look. Wise drivers will remember that just a small amount of moving water truly can move a car and threaten lives. So when it comes to floodwaters on the road, the only safe choice is staying dry.
