Dogs are born to run. Fast. Much of their physiology is geared for speed due to their wolf ancestry, as wolves rely on the ability to pursue and take down prey on the run. Even though a dog’s running prowess is rooted in predatory needs, this very ability can also cause severe injury or even death for the dog.
Such was the case for Moon, a greyhound who died after colliding with a golden retriever at a dog park. Apparently the force of the collision hurtled Moon into the air and resulted in a fatal spinal injury — either from the collision itself or upon impact with the ground. While this may sound like a freak accident, the potential for speed-related injury is very real among dogs.
Speed can kill. It’s not the dog’s fault — it’s physics that deserves the blame.
The key to surviving any impact — whether a dog-on-dog collision, a fall off a ladder, or even a car accident — is the dissipation of energy. Objects in motion possess kinetic energy (KE) and this energy has to be dissipated somewhere if that object suddenly comes to rest or changes direction abruptly due to an impact. Under normal circumstances there’s enough time to gradually slow down where the kinetic energy is usually dissipated as heat, such as heat from a dog’s muscle contractions as they decelerate from a run to a walk, or heat from the friction of a car’s brakes. However in an impact scenario the kinetic energy has to dissipate very quickly, often via physical crushing or fracturing such as broken bones or crumpled fenders.
Where speed comes into play is in the formation of kinetic energy, the formula for which is:
…where m = mass and v = velocity. The relation to notice is that if you double an object’s mass then its KE is also doubled; however, if you double an object’s velocity then its KE is quadrupled.
Most larger dogs weigh 50-100 pounds, which is generally half of what an adult human weighs. We’re twice as massive as dogs yet you don’t see football players dying from making a tackle (although there are certainly lots of severe injuries in that sport). There are three main reasons for this: 1) football players wear padding, 2) the larger mass of human bones, muscles and tissues can absorb more impact energy before injury, and 3) humans are slow; we can’t run fast enough to build up a lethal amount of kinetic energy.
To illustrate this concept let’s compare a greyhound to an NFL player. For this exercise I chose Detroit Lions linebacker Ernie Sims. Why him? He’s big, strong, fast, and hard-hitting — a fine example of kinetic energy unleashed upon impact. I also chose Ernie Sims because he’s an animal lover, a responsible pet owner, and plans to become a veterinarian after his football days are over. A refreshing representative for the NFL compared to a more infamous dog abuser.
During the NFL combine (a sort of tryout mini-camp) Sims weighed 231 pounds and ran the 40 yard dash in 4.55 seconds, good for almost 18 mph. In order to use standard units of measure for energy — the Joule — I converted to metric. Sims weighs 105 kg and runs 29 km/h (8 meters per second), yielding a total KE of 6783 Joules.
A greyhound, in comparison, typically weighs 30 kg (about 66 lb) and can run over 65 km/h (about 40 mph, or 18 meters per second) and thus can generate an impressive 9785 Joules of kinetic energy, 44% more energy than Ernie Sims. A quarterback would rather take a sack from a blitzing linebacker than the impact of a blitzing greyhound!
The true lesson here isn’t the physics so much as it is the caution to be heeded when exercising your dog off leash. Be careful when dogs are chasing each other and if they get too carried away and start to crash into each other, intervene and calm them down. Remember that mentally and emotionally dogs are similar to young children and have the judgment to match. Luckily for parents, toddlers can’t run fast enough to hurt themselves too badly when they display similar poor judgment and slam into a wall, even if they do cry for a while.
While large dogs are generally both faster and heavier than small dogs and thus more susceptible to high speed injury, small dogs are also at risk. Even little terriers can easily top 20 mph, a speed that many humans can’t reach. A couple years ago playing softball my teammate and I collided while running full speed chasing a fly ball. It hurt. A lot. We were “speeding” along at only 10-15 mph yet our collision was truly scary and not something I want to repeat.
I should also mention the potential for dog-human collisions. I’ve noticed that dogs love to use human legs to “set a pick” when getting chased by another dog, where the chased dog runs very close to a person’s legs hoping to force the pursuing dog to deviate around the human. The chasing dog can be so focused on its target, however, that it sometimes fails to notice the pair of legs in its path and slams right into your knees. Be alert for this, although the safest thing to do is simply stand still and bend your knees. Moving around makes you less predictable — the dog is expecting you to stay put — while bending the knees makes them more able to absorb impact without injury. Or you could sit on a bench or stand against a wall or fence and you’ll be just fine.
It’s hard to convince a dog to slow down but that’s OK — dogs should be allowed to run full speed once in a while. My suggestion is to allow a dog’s blazing speed to occur in more controlled settings such as an open field, as opposed to a crowded dog park or heavily wooded terrain, where dogs would be at increased risk for colliding with other dogs, people, or even trees. Dogs are as quick and agile as they are fast and continue to amaze us with their ability to dodge and weave at full tilt, but even they can make a mistake and when they do, the high speed can result in a serious high impact.
Photo: Amanda Schrauben