Bad gas. Loose / worn lifters.
gravity
erosion
loose timing belt, low transmission fluid in transaxle.
gravity causing by rock or sediment to move downhill
gravity causing by rock or sediment to move downhill
A force can change the object's position by causing it to move, its shape by deforming it, and its speed by accelerating or decelerating it.
Gravity is the key force pulling an avalanche downhill. As snow accumulates on a slope, it can reach a critical point where the force of gravity overcomes the friction between layers of snow, causing the avalanche to slide downhill.
friction
Gravity is the force that moves sediment in a mass movement downhill. The force of gravity acts on the weight of the sediment, causing it to slide, flow, or fall downslope.
In a downhill area, you should always park with the front wheels toward the curb. The theory is that if the brakes malfunction, the car will move towards the curb and stop, instead of going downhill, gathering speed and causing an accident.
The force of gravity causes a ball to roll downhill. As the ball is positioned higher up the slope, gravity pulls it downward, causing it to accelerate and gain momentum as it rolls downhill. Friction may also play a role in slowing down the ball's movement.
Bad tire? Rotate and see if thumping changes