How Does a Zip Line Work?

A friend asked you to go ziplining with them this weekend. You see no reason to say no, but you’d like to be a little more educated about the process before your trip. When you zipline, how exactly does the whole thing work?

A zip line works mostly through gravity, with you starting at a high point on the platform and then riding a cable system down to a lower point. Less friction between the pulley and cable increases your terminal velocity so you can ride quickly. The zip line will include brakes as well so you can come to a safe stop.

If you want to learn even more about how zip lines work, you’ve come to the right place. In today’s article, we’ll review the parts of a zip line, the science and physics behind ziplining, and how zip line brakes function. You’ll be all ready to ride by the time you’re done reading! 

The Parts of a Zip Line

It’s hard to explain how a zip line works without first identifying the various parts of the zip line system. Here’s what you need to know.


Although you’re not in a seat when ziplining, you do ride in a seated position. The vehicle that you’re in, so to speak, is known as the trolley. Most trolleys are sized to your body mass, and the size of the trolley can influence your ziplining speed. You usually don’t have to worry about selecting the right trolley size, as that’s the responsibility of the ziplining company. 


As we touched on in the intro, the whole crux of ziplining is that you start at a higher point and then glide your way down to a lower point. Those two points are platforms. The top platform should be designed at such a height topographically that gravity can take hold once you begin riding down the line, as this will give you a more satisfying ride. The width of the platform should let you stand comfortably without feeling like you’re teetering off the edge. 


We’ll have a whole section on how zip lines stop, but we do want to mention now that yes, brakes are a part of the ziplining system. If anything, the ziplining company should provide a primary set of brakes and then a set of backup brakes that become operational if the first set stops working for any reason. 


The cable is the zip line itself. We just wrote a great introductory post on zip line cables that you should check out if you missed it. Most zip line cables are made of galvanized wire rope that’s built stronger than even stainless steel. Each cable in the rope comprises a series of smaller cables for greater durability. The galvanized rope is attached to a pulley, and the pulley is what guides you down when you go ziplining. 

How Does a Zip Line Work? How Science Plays a Role

Okay, so now that we’ve gotten that explanation out of the way, let’s talk about the way a zip line works. First of all, when you arrive at your ziplining destination, you’re outfitted in a harness and then clipped onto the ziplining cable. Remember, the cable itself is attached to a pulley, and the pulley system is what moves you from the first platform to the second. 

Well, that and gravity. If we didn’t have gravity, then when you stepped off the platform, you would just hang there. Fortunately, that’s not what happens at all. The slope-like design of the zipline from the higher platform to the lower platform pulls you down. 

It’s not just gravity at play here, but inertia as well. This physics property determines that matter will continue moving in a straight line until an external force stops it, such as the brakes of the zip line. 

You don’t have to worry about going slowly when ziplining. The pulley system controls friction as you ride, which allows you to get the kind of speed that thrill-seekers enjoy. The reason for this is that, compared to sliding, rolling down the zip line produces less friction. Since friction has a greater force than gravity, you need that lesser degree of friction.  The steeper the zipline, the faster you’ll usually go, but we’ll talk more about speed a little later, so make sure you check that out! 

How to Stop a Zip Line

You’re whizzing along the zip line at a pretty good speed. You’re really enjoying yourself, but now you’re beginning to wonder when and how you’re going to come to a stop. Well, as we mentioned earlier, the zipline system has brakes as well as a backup set of brakes. The brakes can be active or passive. With active brakes, you can manually slow yourself down. This comes in handy when going down steep slopes or if you have a high max velocity.

What you’ll see far more often when ziplining are passive brakes. These brakes are not controlled by riders. Instead, the design of the zip line course is such that the line naturally tapers to bring you to a stop. 

When you stop like this, several physics properties are at play. One of these is the friction of the line. If you’re using active brakes as part of the zipline system, then you’ll wear gloves so you can increase friction to make the zip line slow down. Remember, friction’s force is stronger than gravity’s, which is why you can slow yourself down using this method.

The second physics force that helps you stop when ziplining is air resistance. What is air resistance, you ask? It’s a fluid dynamics theory that tells us that drag works oppositely of relative motion on any moving object and its surrounding fluid. There’s a whole complex air resistance formula that involves constant velocity, drag, and air density.

The long and short of it is this. When an object in motion travels quickly, such as your zip line, its air resistance increases. As this happens, your zip line achieves terminal velocity, which influences the speed of a free-falling object when its resistance prevents the object from increasing in further speed. In other words, when ziplining, terminal velocity determines what your max speed will be. 

With more air resistance applied on the zip line, your speed begins to slow down, eventually coming to a stop. So sure, you could say that the brakes helped you stop, but there’s a lot more science at play than you might have realized! 

How Fast Do You Go When Ziplining?

Like we said we would, let’s get into a discussion of ziplining speed now. The average speed when riding a zip line is anywhere from 21 to 30 miles per hour to 31 to 40 MPH and sometimes as high as 50 MPH. Why the speed discrepancy, you’re probably wondering? How fast you can travel on a zip line comes down to several factors, so let’s get into those now. 

How Long the Line Is

Taking a short zip line ride won’t let you reach high speeds to the same degree as a longer ride. The more time you have on the zip line, the closer you can get to achieving terminal velocity. This is because gravity and inertia have more time to work. 

The Slope Angle

Even on the longest zip-lining ride, if there’s no slope or if the slope is very unpronounced, then you won’t go fast. Remember, gravity is a downward-pulling force, which means you have to be higher up for gravity to do its thing. Not only that, but your terminal velocity surges as the slope angle does, which again increases the speed of your ride. 

Your Weight

The last factor that affects your ziplining speed is your weight. Although you might think that someone who weighs more is bound to travel down the line more slowly, the opposite is true. An object that weighs more has greater terminal velocity compared to a lighter object since its force of gravity is greater. The object will achieve terminal velocity more easily and reach its max speed potential in less time. 

Final Thoughts

When ziplining, you stand on a high platform and then ride down a line that’s attached to a pulley system. Such physics principles as gravity, inertia, terminal velocity, and air resistance all influence how fast you’ll go, but those aren’t the only factors that have an effect. Your weight, the angle of the slope, and the length of your ride can also influence your speed. Even stopping the zip line is scientific, requiring air resistance and friction. 

We hope that learning about how zip lines work makes you feel confident enough to schedule a ziplining experience today! 

Geoff Southworth

I am a California native and I enjoy all the outdoors has to offer. My latest adventures have been taking the family camping, hiking and surfing.

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