What happens when you drop something?

When an object falls freely under gravity (no air resistance), it accelerates downward at a constant rate. On Earth, this acceleration is always g = 9.81 m/s².

Key Equations

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Real-world example

A ball dropped from a 100-meter building takes about 4.5 seconds to hit the ground and reaches a velocity of about 44 m/s (158 km/h)!

What if you throw it upward?

When you throw an object upward with initial velocity, gravity still pulls it down. The object slows down, stops at the peak, then falls back down with increasing speed. Acceleration of Gravity is ALWAYS acting on this object!

Key Equations

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Key insight

Time to reach max height = Time to fall back down. This is because gravity acts equally in both directions!

What is acceleration?

Acceleration is the rate of change of velocity. When a car speeds up from 0 to 100 km/h, it's accelerating. Constant acceleration means it speeds up at the same rate every second.

Key Equations

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Real-world context

A car with 5 m/s² acceleration goes from 0 to 60 km/h in 3.3 seconds. Faster accelerations mean quicker speed-ups!

What happens when you brake?

Deceleration is negative acceleration — velocity decreases over time. When a car brakes, it's decelerating. The faster you're going, the longer it takes to stop at the same deceleration.

Key Equations

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Safety lesson

At 30 m/s (108 km/h) with 5 m/s² braking, you need 90 meters to stop. Double the speed → 4× the stopping distance!