I have a fairly rudimentary understanding of gravity but was under the impression that two objects of different mass (say an anvil and a ping pong ball) dropped together would accelerate at the same rate and hit the ground together. So why, when I freewheel down a hill behind my much lighter girlfriend, do I always catch her up and have to brake?

More massive objects fall faster than less massive objects because they are acted upon by a larger force of gravity; for this reason, they accelerate to higher speeds until the air resistance force equals the gravity force.

Wind resistance.

You will both have similar wind resistance and friction to overcome, you have more mass so more force to push you along( as well as more inertia to overcome) so you have greater acceleration. The ping pong ball and the anvil will only fall at the same rate in a vacuum.

So I was completely wrong then?

did she accuse you of having a more expensive bike?

Ignore druidh, he’s wrong. All thing fall at the same rate regardless of mass – heavier objects do not fall faster.

However, objects with large area are subject to more wind resistance, so if you weigh more but don’t need to punch a bigger hole in the air you will accelerate faster and have a higher terminal velocity.

You should see us on the tandem – it flies down hill. Freewheeling in a bunch it is funny how much faster it is

You have some of the picture…

In a system free of resistive forces (air resistance is the main one in this case), objects will tend to accelerate at the same rate, regardless of mass.
There’s a greater force of gravity acting for more objects of higher mass, but there’s a correspondingly greater force required to accelerate.

Effectively, you freewheel faster because the air doesn’t slow you down as much.
There’s a similar air resistance acting on you both (you will have similar cross sectional areas facing the direction of motion), but it takes more force to slow you down by the same amount (because you’re heavier) – as you’re slowed down less, you roll faster 🙂

Plus there could be hundreds of other differences, like tyre pressures, suspension travel helping to iron out uneven-ness, rolling resistance of tyres

Is she blocking the wind?

Does she have the same bike as you?

Bearings, tyres-too many varibles.

She’s pumping the brake? lol

Women always drag the rear brake….. 😆

<duck and cover>