Why Physics Makes You Faster
You’ve been told to “move your legs faster,” to “pump your arms,” to “get up on your toes.” Some of that is useful. Most of it is incomplete. What nobody ever shows you is why these things work — or why the conventional wisdom often leads athletes in completely the wrong direction.
Speed Simplified fixes that. This course is built on physics and geometry — Newton’s Laws, force vectors, the stretch-shortening cycle, the strength-to-weight ratio — but you won’t need an engineering degree to follow it. Every concept is built from the ground up with plain language, memorable analogies, and real numbers that make the ideas stick.
The result is a framework that explains every training decision: why to lean in the blocks, why long static stretching before a sprint backfires, why the strongest athlete isn’t always the fastest, and why a bouncy tendon beats a bigger muscle. Once you understand the physics, you have a filter for any coaching cue you’ll ever hear for the rest of your career.
What This Course Covers
- Force, Direction & Time — the three variables under every step you take
- Acceleration Geometry — why lean and shin angle determine how fast you launch
- Max-Velocity Mechanics — why top speed looks nothing like acceleration
- The Human Spring — how tendons store and return energy for nearly free
- Stride Length vs. Frequency — the trade-off and the overstriding trap
- Posture & Alignment — how a kinked hose loses pressure and a bent body loses force
- Arm Action — rhythm engine and rotational balance, explained by angular momentum
- Speed Myths Debunked — physics exposes the most common bad advice in the sport
- Strength-to-Weight — Newton’s Second Law applied to your training
- The Blueprint — combining all the ingredients into a real training week
What Makes You Fast: Force, Direction & Time
Ask almost anyone how to run faster and you’ll hear the same thing: “move your legs faster.” It feels obvious. It’s also mostly wrong. The athletes who win aren’t winning a leg-speed contest—they’re winning a contest of how hard they hit the ground, which direction they aim that force, and how little time they take to do it. Get those three things right and speed takes care of itself.
The Core Idea
There’s one equation under everything in this course:
Speed = Stride Length × Stride Frequency
That’s just: how far you travel with each step multiplied by how many steps you take each second. To get faster, you make each step cover more ground, take steps more often, or both.
But here’s the part that changes how you train. You don’t make a stride longer by reaching your foot out in front of you. You make it longer by pushing harder into the ground. Every step, the ground pushes back on you with exactly as much force as you put into it. That push is what launches you into your next stride.
This is Newton’s Third Law — for every action there is an equal and opposite reaction — and it’s the single most important sentence in sprinting. You don’t run on the ground. You run against it.
The force you press into the ground is called ground reaction force (GRF). Researchers have repeatedly shown that faster runners reach top speed by applying greater force to the ground (relative to their body weight), not by swinging their legs through the air more quickly. Sports scientists studied 33 runners of different speeds and found that the fastest ones (about 11.1 m/s top speed) applied roughly 1.3× the force (per body weight) that slower runners (6.2 m/s) did, yet their leg-swing times in the air were nearly the same. This landmark work by Peter Weyand and colleagues showed that top speed is set primarily by how much force you can put into the ground quickly. Newton’s Third Law—“for every action there is an equal and opposite reaction”—is the single most important concept in sprinting. You run by driving into the ground and letting it drive you back.
Now Add Direction and Time
Direction. Force is not just a number — it’s an arrow. It has size and a direction. Push straight down and you bounce in place. Push down and back and the ground sends you forward. So where you aim your force matters as much as how big it is.
Time. Speed is a race against the clock on every single step. The faster you go, the less time your foot spends on the ground—so you have a smaller window to deliver that big push. Fast athletes learn to apply a huge force in a tiny fraction of a second. In physics, force × time = impulse, and it’s what actually changes your speed.
Think about turning at the end of a lap. You plant your feet on the wall and shove. The wall doesn’t move — it shoves you back just as hard, and you glide away. The harder you push, the farther and faster you go. Your foot and the track work exactly the same way.
Each time you push your foot against the pavement, the board rolls forward. A weak little tap barely moves you; a strong push down and back sends you gliding. Sprinting is just doing that with your whole body, over and over, very fast.
- Youth “Push the ground away from you.” Play games that reward a hard first push (push-up starts, partner-resisted starts). One cue is enough.
- High School Start feeling the difference between reaching with the foot (slow, braking) and pushing through the ground (fast, propulsive).
- College / Pro Think in terms of impulse and force orientation — maximizing force in the available contact time and aiming it for the phase you’re in.
Stand arm’s length from a wall, hands on it, body in a straight line leaning toward it. Drive one knee up, then push that foot down and back into the floor like you’re shoving the floor behind you. Alternate legs. Feel that the power comes from pushing into the ground, not from lifting your knee. This is the whole sport in one drill.
Key Takeaways
- Speed = how far each step goes × how many steps per second.
- You don’t run on the ground; you run against it — push hard, get pushed back.
- Force has a direction (aim it back, not just down) and happens in a tiny window of time.
- Faster athletes apply more force in less time<, not just faster-moving legs.