Last Sunday (20th March) marked the anniversary of Sir Isaac Newton’s death and, while he died over 250 years before mountain biking was invented, his legacy is of use to us all. Newton is famous for discovering gravity and, as a blogger who’s interested in gravity-assisted mountain biking, his work has got to be worth a look. Gravity is a force, forces make things move and Newton’s Laws of Motion go something like this:
Newton’s first law – The Law of Inertia
A lot of people think inertia is the ‘resistance’ you have to overcome to get an object moving but Newton’s law of inertia is more than this. Inertia refers to the tendency of an object to keep doing the same thing ie if an object is still it will stay still unless a force moves it but if an object is moving it will keep moving (at a constant speed, in the same direction) until a force slows it down or change it’s direction.
You come up against the first part of this law when you’re initially stomping on your pedals to try and get you and your bike moving. Trying to get moving can be hard going as you have to overcome the tendency of you and your bike to stay still. Once you’re up to speed on a flat trail though, it’s pretty easy to keep travelling at that constant speed and if you stop pedalling you’ll freewheel along until friction and drag etc slow you down (2nd part of the law). A more scary example of inertia is when you’re carrying too much speed into a corner. The bike wants to keep going in a straight line and you have to use forces eg friction, to slow the bike down or try and wrestle it the way you want to go around the corner.
Newton’s second law – Force = Mass x Acceleration
To overcome inertia Newton explained that we need forces and forces make things accelerate. The bigger the force, and the lighter the object, the greater the acceleration will be.
Within downhill, the masters of manipulating this law are the members of the Steve Peat Syndicate. While other riders are known for their all action, aggressive riding styles ie putting a lot of energy into pedalling, to create the forces needed to accelerate them down the hill quickly, Steve Peat, Greg Minnaar and Josh Bryceland are all renowned for winning races with a minimal number of pedal strokes. To put it another way, when we talk about ‘flow’ or ‘riding smooth’ what we’re really talking about is mastery of force manipulation and these guys have it in spades. They use technique to put their body mass in the right place, at the right time to harness forces to create acceleration. Want an insight in to how they do it? Read on for Newton’s third law.
Newton’s third law – Every action has an equal and opposite reaction.
I mentioned him above so I may as well use him again, as Josh Bryceland (and in particular his left ankle) felt the effect of this law when he sent that massive jump off the bridge at the end of the 2014 World Champs in Hafjell. As Ratboy and his bike landed, the earth
provided an equal and opposite push back against them. As the earth’s heavier than he is, he didn’t displace the earth and the forces that were sent back up through him and the bike snapped his ankle.
This isn’t the enemy of us all though. We use this law to our advantage (in combination with the other two laws above) when cornering, jumping & pumping etc. In the case of pumping, by forcing the bike down into the ground, the ground pushes back. As the law of inertia tells us, the tendency of objects is to keep moving in the same direction so the forces we create continue to push us forward but, as we know from the second law, forces make things accelerate so the extra forces we generate by the pumping action fire us down the trail. Want to see this in action? Watch Aaron Gwin win a world cup downhill race without making a single pedal stroke.
The conclusion to this therefore is a raise of the glass in the direction of Mr Newton. To many these physics principles seem a bit abstract but if you take the time to, at least in part, understand them the benefits to your riding will be significant.