Meet the Forces
What is a force?
A push or a pull acting on an object, characterized by both a magnitude (strength) and a direction.
What is the acceleration of an object if all the forces acting on it are perfectly balanced?
Zero (the object will remain at rest or continue moving at a constant velocity).
In what direction does friction always act relative to a moving object?
In the exact opposite direction of the object's motion.
What is gravity?
An attractive, non-contact force that exists between any two objects in the universe that have mass.
What is inertia?
The tendency of an object to resist any change in its current state of motion (described by Newton's First Law).
How do physicists visually represent the strength and direction of a force on paper?
By using force vector arrows (where the arrow points in the direction of the force, and the length represents its strength).
What is net force?
The vector sum of all the individual forces acting on an object.
What microscopic reality causes friction between two surfaces that look smooth?
Microscopic peaks, bumps, and rough ridges that catch and lock against each other.
What two properties dictate the structural strength of gravitational pull between two bodies?
Mass and distance (greater mass increases gravity; greater distance decreases gravity).
What physical property directly determines how much inertia an object has?
Its mass (more mass = more inertia).
What is a Newton (N)?
The standard metric unit used to measure the magnitude of a force.
If one student pushes a heavy desk to the right with 40 N of force, and another pushes it to the right with 30 N, what is the net force?
70 Newtons to the right (40N + 30N).
What is static friction?
The friction that acts on an object that is at rest, preventing it from starting to move (it is typically stronger than sliding friction).
What is the difference between mass and weight?
Mass is the amount of matter inside an object (stays constant), while weight is the measure of the gravitational pull acting on that mass (changes by location).
Why is it much harder for a fully loaded freight train to come to a stop than a standard car traveling at the same speed?
The train possesses vastly more mass, meaning it has significantly more inertia and requires much more force/distance to stop.
What are non-contact forces?
Forces that can act over a distance without physical contact, such as gravity, magnetism, and electric forces.
A crate is pulled to the left with 150 N of force and to the right with 200 N of force. What is the net force?
50 Newtons to the right (200N - 150N).
What is fluid friction?
Friction that occurs when an object moves through a fluid (liquid or gas), such as air resistance or water resistance.
Why does a human weigh significantly less on the Moon than on Earth?
The Moon has much less mass than Earth, resulting in a much weaker gravitational field pulling down on your body.
According to Newton's Second Law (F = ma), if you keep the mass constant but double the net force applied, what happens to the acceleration?
The acceleration doubles.
What is the normal force?
The supportive contact force exerted by a surface perpendicular to the object resting on it, which balances out gravity.
If a car is traveling in a straight line at a perfectly constant speed of 45 mph, are the forces acting on it balanced or unbalanced?
Balanced (because there is no acceleration, the net force must be zero).
Why does an open, flat sheet of paper fall slower through the air than a tightly crumpled ball of paper of the exact same mass?
The flat sheet has a larger surface area, which forces it to collide with more air molecules, generating a greater upward force of air resistance.
What is terminal velocity?
The maximum constant velocity reached by a falling object when the upward force of air resistance perfectly balances out the downward force of gravity.
What is the acceleration of a 2 kg skateboard when pushed with a net force of 20 N?
10m/s^2 (Acceleration = Force/Mass = 20N/2kg)