Answer:
1. By performing an experiment.
2. By calculating it using law of gravitation.
Step-by-step explanation:
Method 1:
Step 1: First you need a timer, a ball and a smart phone with camera.
Step 2: Go to, say, third floor of your school building, drop the ball and start the timer.
Step 3: Take a shot every 1 second until the ball reaches the ground.
Step 4: Check your photo. Pay attention to where it reaches at every second. Try to measure the distance it goes from the top. Ex: t = 1, d = ?, t = 2, d = ? ...
Step 5: Since velocity = distance / time, now you can calculate like v1 = d1 / t1, v2 = d2 / t2 ...
Step 6: Since acceleration = velocity / time, now you can calculate a1 = v1 / t1, a2 = v2 / t2 ...
Step 7: Repeat this measurement for several times, and you'll find the average acceleration of gravity to be nearly 9.8 m/s^2.
Method 2:
We can simply apply the equation for getting the acceleration of gravity:
g = GM/r^2,
where G is the gravitational constant, M is the mass of Earth, r is the radius of Earth (since you probably need to know the acceleration of gravity near the surface of Earth).
Let's plug numbers in:
g =
Try to calculate this, and you will get that g = 9.8 m/s^2.