Conceptual Questions related to Newton's First Law of Motion

Newton's First Law of Motion

Que: An object that is not accelerating or decelerating has zero net force acting on it.
True
False
If all the forces net out, then the object's velocity will not change. This is just a restatement of Newton's First Law of Motion.

Que: The only way to slow down a moving object is to apply a net force to it.
True
False
Velocity will only change if a net force is applied. In this case, you'll slow the speed of the object if you apply a net force in the direction opposite its direction of motion.

Que: Objects in orbit around the Earth (like a satellite) still have net forces acting on them.
True
False
An object with no net forces acting on it would not have a change in velocity. If it is stationary, it would stay stationary. If it is in motion, it will stay in motion with a fixed velocity (moving in a straight line). This comes directly out of Newton's First Law of Motion.
An object in orbit may have a constant speed, but its direction is constantly changing as it moves in a circle (or ellipse) and, thus, its velocity is also changing (remember, velocity takes into consideration speed and direction). Therefore, there must be a net force acting on it. This is the net force of Earth's gravity acting on the object.
For the most part, we can assume a vacuum in "space" near Earth, but it is not actually an absolute vacuum (there is just a very low density of molecules). It isn't the intent of this question, but bumping into those very sparse molecules does apply a very small net force on a satellite as well which would, over time, slow it down.

Que: When no net force is applied to a moving object, it still comes to rest because of its inertia.
True
False
If no net force is applied to a moving object, its velocity will not change. The reason why we observe objects coming to rest, say when we push them on the table, is because the force of friction is decelerating it. Inertia is not a force. It is the tendency of an object to resist a change in its velocity.

Que: Objects tend to stay moving because of a force called inertia.
True
False
Inertia is not a force. It is the tendency of an object to resist change in velocity. Mass is a measure of an object's inertia.

Que: An object's inertia causes it to come to a rest position.
True
False
Inertia is the tendency of an object to resist change in velocity. It is not a force that causes an object to accelerate or decelerate. A moving object with a lot of inertia (measured by its mass) would actually require more net force to change its velocity in a given amount of time than an object with a low inertia.

Que: A stationary object has no forces acting on it.
True
False
When you push on a stationary object, you are applying a force. Despite this, you still might not be able to accelerate it. That is because there might be another force that nets against yours.
For example, you push on a beached whale. The reason why you can't accelerate it is because the force of friction between the whale and the sand perfectly nets against (same magnitude, opposite direction) the force you are applying.
For another example, you're presumably not plummeting to the center of the Earth right now despite the fact that Earth's gravity is pulling on you. This is because your chair is exerting a normal force in the opposite direction (radially outwards from the center of Earth) that perfectly offsets the force of gravity.
This statement would have been true if it said "net forces", not just "forces".

Que: When an object is stationary, all of the forces acting on it are balanced.
True
False
When you push anything, you are applying a force. Despite this, you still might not be able to change its acceleration. That is because there might be another force that balances against yours (netting to 0 net force).
For example, you push on a beached whale. The reason why you can't accelerate it is because the force of friction between the whale and the sand perfectly nets against (same magnitude, opposite direction) the force you are applying.
For another example, you're presumably not plummeting to the center of the Earth right now despite the fact that Earth's gravity is pulling on you. This is because your chair is exerting a normal force in the opposite direction (radially outwards from the center of Earth) that perfectly offsets the force of gravity.
If the forces were not balanced, then the stationary object would accelerate.

Que: A ball is moving upwards and to the left. The net forces acting on it are also upwards and to the left.
True
False
Not enough information
If we are on Earth, then the net forces are downward due to Earth's gravity (and possibly down and to the right due to air friction).
If the ball is traveling through space, it could maintain that constant velocity without any net forces.
Remember, the net forces change velocity. The existence of movement alone doesn't tell you anything about the net forces acting on it (unless you knew the magnitude and direction of acceleration) so, for this case, there really isn't enough information.

Que: Which of Newton's Laws explains why satellites need very little fuel to stay in orbit?
First Law
Second Law
Third Law
Once a satellite is in orbit, the only net force acting on it is the inward force of gravity. The tangential speed of the satellite is just right so that gravity only has the effect of changing the direction of travel. It is a near vacuum in space so the satellite encounters almost no friction to slow them down.


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