A Physics Primer: Part 2

Newton in a Nutshell

     In the previous article (click to read Part 1: Getting Grounded), I introduced 2 properties found in all objects: Center of Gravity and Base of Support. I also showed how you can apply these concepts to your workouts to make them more efficient and effective. Let’s continue on your physics journey with a look into the incredible world of Sir Isaac Newton and that all-important force, gravity.

Gravity

     A constant downward force that acts on all objects at a rate of 9.8m/s². Gravity is the reason why your keys fall straight down when dropped and a punt in football eventually lowers to the earth. This constant force also causes a downward line of pull of our dumbbells and other weights in the gym. Keep gravity in the back of your mind when you read about Newton’s laws because it is always acting on us and influences how we are able to manipulate objects and ourselves in space.

Newton’s First Law of Motion

     An object at rest (or in motion) will remain at rest (or in motion) unless acted upon by an outside force great enough to change its state. This law is also referred to as the law of inertia. There are two types of inertia: static and dynamic. When an object is at rest it has static inertia. When an object is moving it has dynamic inertia.

Real-life example:

     Your sofa is resting peacefully against the wall—it contains static inertia—and you have no reason to pay attention to it until you accidentally kick your favorite toy car underneath it. Now, you must lift the heavy object to recover that gift from aunt Suzy by applying a force greater than the one keeping the couch still. Essentially, you must change the inertial state of the sofa (from static to dynamic) to raise it off the floor, delicately sweep the toy out from underneath, and return the sofa back to its resting state on the ground.

A girl’s gotta do what’s necessary to retrieve her play toys.

[This law applies to couch potatoes too. The longer they lounge the harder it is to get them moving. It takes a large outside force—i.e. the promise of a hot date or a beer run—to change their inertial state from static to dynamic.]

Gym example:

     You are about to squat with 20lb dumbbells in your hands. In honor of Newton, the major inertial phases are broken down into separate subroutines.

1. Just standing still (static inertia) requires you to resist the downward pull of gravity and the 40 extra pounds on top of your own body weight.
2. You begin the descent and, assisted by gravity, have overcome static inertia and have now generated dynamic inertia—this part feels pretty easy.
3. When you near the bottom of a squat you must stop your descent, which requires a change from dynamic to static inertia, in addition to resisting gravity’s desire to keep lowering you towards the ground. Now, you have stopped at your lowest point.
4. In order to stand back up, you must make the transition from static to dynamic inertia while fighting gravity and its downward pull on the weight throughout your ascent.
5. Once you get to the top and have finished the rep—shifted from dynamic to static inertia—you can thank gravity for the assist because it helped you come to a stop at the top.

The picture on the left shows Jack at the hardest part of the squat because he’s contending with gravity, the weight, and must overcome static inertia to stand back up.

     Pay attention to the inertial transitions in your workouts because those instances often require the most effort to implement effectively. The best athletes can start, stop, and change directions with excellent precision and minimal wasted energy.

Newton’s Second Law of Motion

     The force applied to an object (mass) produces a proportional acceleration. Another way to say this is that if an object is accelerating then there must be a force acting on it. The greater the mass of the object, the greater the amount of force needed to accelerate it. For example, if you wanted to move the big couch, you’ll need to apply a lot more force than if you wanted to lift a small chair. Likewise, you can accelerate the lighter object much faster because it has less mass. The equation that sums up this law is:

Force=mass x acceleration

     In the gym, most people tend to think of increasing strength (force production) solely by raising the weight (mass). However, by using Newton’s formula you can also increase force by increasing the acceleration. Take the bench press as an example : You complete one rep with 100 pounds in 2 seconds. You have two options to increase your force output, according to F=ma. 1) Increase the weight or 2) Increase the speed. So, you could load up another 50 pounds on the bar and take the same 2 seconds to finish the lift or you could keep the 100 pounds but complete the rep in 1 second. Either way you come out with a net improvement in force production.

Either load up or speed up to increase your force production.

     It’s important to mix up your methods so that you stimulate different muscle fiber types, energy systems, and neurological adaptations.

Newton’s Third Law of Motion

     For every action there is an equal and opposite reaction.

     You have probably heard something like this before and this happens to be my favorite of the 3 laws. How does it work in real life? Well, how do you lift the couch to get that toy car? You apply an active force into the ground with your legs and the ground pushes back up into you (reactive force), allowing you to summate that force into useful sofa lifting strength. Likewise, in order to get back up from the lowest part of a pushup (elbows bent), you apply active force into the ground with your arms and the ground pushes back an equal amount of reactive force that lifts you up (elbows straight).

You are a result of the forces you apply.

      This one simple concept changed the way I lifted weights and has turned on a light switch for my clients as well. You know those front lunges you’ve been doing? Well, instead of thinking that you lunge forward and then pick up your front foot to return back to your original position, think of it this way: Once you are at your lowest point in the lunge you must apply force down and forward in order for the ground’s reactive forces to push you up and back to your desired end position.

     Consider what position you want to end up in and then apply force in precisely the opposite direction.

     Hopefully, this physics primer has helped lead you to a better understanding of your own movements and how you can apply these principles to your exercises, making you more efficient and effective. Pass this along to others so that we spread a more scientifically-based rationale for movement rather than allowing the plethora of ungrounded fallacies and myths to continue perpetrating popular culture.

Keep on Movin’

-CA