How do you stop a stick of dynamite? If you tow a vehicle behind your motorhome, that’s not a rhetorical question — at highway speeds, the momentum of a 3,000-pound towed vehicle (say, a Ford Focus) has the kinetic energy of a quarter stick of dynamite (425,000 foot pounds of force). A 6,000-pound Jeep Grand Cherokee has the kinetic energy of a half stick of dynamite (850,000 foot pounds of force). And, a 10,000-pound Chevy Silverado has the kinetic energy of three-quarters of a stick of dynamite (almost 1,500,000 foot pounds of force).

That’s according to the law — the second law of motion.

Like every other law of physics, the second law of motion — “force equals mass times acceleration” — isn’t open for debate. “Mass” (the weight of the towed vehicle) times “acceleration” (65 miles an hour, in the examples above) equals “force.” Always. Which creates, in effect, a 3,000- to 10,000-pound battering ram aimed directly at the back of the coach. 
  

Learn more about why supplemental brakes are necessary

The laws of physics don’t recognize state boundaries. So it doesn’t matter whether you’re towing in Texas, Massachusetts or British Columbia — there’s no getting around the long arm of the second law of motion. Or, for that matter, the third law of motion — “for every action, there is an equal and opposite reaction” — every time you hit the brakes. But even if you had an extra two or three tons of braking capacity, the weight of a towed vehicle isn’t over the motorhome’s brakes. It’s pushing on them from behind.

So it’s not surprising, then, that safety is the number one reason most people add a supplemental braking system. Supplemental brakes take the load off the motorhome, and the motorhome and the towed vehicle brake in tandem, taking significantly less time and distance to come to a controlled stop — approximately 34 percent less, according to a study* by ROADMASTER (see the “Test Results at 50 mph" chart).
  
Supplemental brakes also relieve stress on the tow bar and the mounting brackets — a panic stop without supplemental brakes is a leading causes of tow system failure. They also keep the combination straight as you brake, so there’s less chance of a “jackknife.” And supplemental brakes reduce the chance of a catastrophic brake failure at the motorhome, as a result of sustained braking — for example, when you’re driving down a steep grade in the mountains.

Safety notwithstanding, there are several other compelling reasons to add supplemental brakes…

It’s required — To one degree or another, every state and province in North America has recognized what the second law of motion implies. Which is why supplemental brakes are required in virtually every state and province. The majority of states, plus many Canadian provinces, specify 3,000 pounds as the maximum weight which can be towed without supplemental brakes, according to the American Automobile Association.
  
There’s currently no national standard, and the towed weight limits vary from state to state (and in Canada, from province to province) — 4,500 pounds in Texas, 10,000 pounds in Massachusetts, and 3,080 pounds in British Columbia (again, according to the American Automobile Association).
  
There is, however, that universal standard — “force equals mass times acceleration.” Whether you’re in Texas, Massachusetts or British Columbia, every towed vehicle combination is always in compliance with the second law of motion.
  
Chassis warranty and liability — Some motorhome chassis manufacturers will void your warranty (and insurance adjusters will void your policy) against damage claims if you tow without supplemental brakes. Workhorse will void your chassis warranty if you tow more than 1,000 pounds without supplemental brakes; Ford stipulates 1,500 pounds.
  
Wear and tear — Supplemental brakes cut down on everyday wear and tear — on the tow bar and the bracket, and on the frame of the towed vehicle. So they last longer. And because they aren’t braking for two vehicles, your motorhome’s brakes last longer, also.
  
It just makes good sense — Every other trailer on the road today has supplemental brakes — fifth wheels, travel trailers, semi-trailers — they all have their own braking systems. When you’re towing a couple of extra tons — or more — shouldn’t you have a supplemental braking system to stop it?