Difference between sped and velocity :

Speed is a scalar and velocity is a vector.
A scalar only has magnitude while a vector has magnitude and direction.

Example: If you are traveling north at 65 miles an hour your speed is 65 miles an hour, your velocity is 65 miles an hour north.
It gets a little more complicated. Speed = distance (a scalar)/time Velocity = Displacement (vector)/time

Example: If you run 5 miles in an hour left and then 5 miles in a hour right your speed is 10 miles/2 hours = 5 miles an hour. However, since you end up in the same exact location as where you started your displacement is zero making your velocity zero as well. Think of it this way; since velocity is a vector it requires a direction if i ended up exactly where I started I have no direction, thus velocity must be zero.

One more example to clarify: If you ran 6 miles right and 4 miles left in 2 hours, your speed will be 5 miles an hour (10/2=5) your velocity would be 1 mile an hour to the right, since displacement is 2 miles to the right (6 to right - 4 to left = 2 to right) and the time is 2 hours displacement/time = velocity; 2 to the right/2 = 1 mile to the right per hour.

Why does a hammer and feather accelerate at the same speed on the moon? they will both accelrate downwards at the same rate if there is no air friction - which is true on the moon.
They both obey Newton's 2nd law which gives us the relationship Force = mass x acceleration. now they both have