Gravity produces force that attracts two bodies with mass to one another.
F = (G * m1 * m2) / d^2.
F - force of mutual attraction
G - gravitational constant, (6.67 E-11 m3 kg-1 s-2)
m1, m2 - masses of bodies
d - distance between their centers of masses
While G is hard to measure with same accuracy as other constants,
anyone can see at home if gravity exists or not.
Use this video as setting:
(it is called Cavendish Experiment)
but do not trust it.
There are lot of videos on YouTube saying two oposite things:
Some say "it worked, this is how".
Others say "this is bullshit, nobody did the experiment after Cavendish".
Well, first ones obviously did.
Anyway,
one side could move beam in stop motion,
other side could hide some blockage to the beam.
Do it yourself to make sure nobody tampers with your stuff.
Use objects heavy enough (with enough mass, both on beam and on floor), so they can act in some acceptable time.
Unless your parents are Flat Earthers and won't let you do it.