PHY Ch. 2
A truck is travelling at 10 m/s. A package drops off the truck. Neglecting air resistance, as the package hits the ground, its horizontal speed is
10 m/s
The gain in speed each second for a freely-falling object is about
10 m/s
the object is in equilibrium, the sum of all the forces acting on the object is zero.
Equilibrium rule
The tendency of objects to resist changes in motion.
Inertia
An object is in a state where there is no change in motion.
Mechanical Equilibrium
A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is
about 30 m/s
A truck is decelerating. A package is dropped from the midpoint of the ceiling of the truck's storage compartment. The package hits the floor
closer to the front of the truck than the midpoint
A truck is moving at constant velocity. Inside the storage compartment, a rock is dropped from the midpoint of the ceiling and strikes the floor below. The rock hits the floor
exactly below the midpoint of the ceiling
You brake suddenly. The passengers in your car lurch forward. This demonstrates
inertia
A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. This best demonstrates that
the milk carton has inertia.
You tie a rock to a string and whirl it in a horizontal circle. The string breaks. In the absence of gravity, the rock
travels in a straight line horizontally away from you
An object falls out of an airplane, and falls freely downward. Its
velocity increases
As an object freely falls downward, its
velocity increases
