1. An object at rest will stay at rest (and an object in motion will stay in motion at a constant velocity) unless acted upon by a net force.
* Condition: Zero net force. This means the sum of all forces acting on the object is zero.
* Example: A book lying on a table is at rest because the force of gravity pulling it down is balanced by the normal force from the table pushing it up.
2. An object's acceleration is directly proportional to the net force acting on it and inversely proportional to its mass.
* Condition: Non-zero net force. The larger the net force, the larger the acceleration. The more massive the object, the smaller the acceleration for the same net force.
* Equation: F = ma (Force = mass x acceleration)
* Example: Pushing a heavy box requires more force to get it moving (and to keep it moving at a constant velocity) than pushing a lighter box.
3. For every action, there is an equal and opposite reaction.
* Condition: This law is important for understanding how forces interact between objects.
* Example: When you jump up, your feet push down on the ground (action). The ground pushes back on your feet with an equal and opposite force (reaction), propelling you upwards.
Here's how these relate to your question:
* Staying at rest: For an object to remain at rest, the net force acting on it must be zero.
* Moving at constant velocity: For an object to continue moving at a constant velocity, the net force acting on it must also be zero. This means the object is not accelerating (either speeding up or slowing down).
* Moving with increasing velocity: For an object to accelerate (increase velocity), there must be a non-zero net force acting on it. The direction of the net force determines the direction of the acceleration.
Key Point: The concept of "inertia" is crucial here. Inertia is the tendency of an object to resist changes in its state of motion. An object at rest will stay at rest because of its inertia. An object in motion will stay in motion at a constant velocity because of its inertia. A force is needed to overcome inertia and cause a change in motion.
