Motion and Forces Study Guide

What is a frame of reference?

A coordinate system that defines the position and motion of objects, serving as a viewpoint (stationary or moving) for measuring properties like velocity and acceleration. It is used to determine if an object is moving.

What is a vector?

A measurement that contains both magnitude (size) and direction

What is acceleration?

The rate at which velocity changes

What is a scalar?

A quantity with only one component: magnitude

What is distance?

The length between two objects, the total path taken from Point A to Point B

What is displacement?

How far you are from where you started, the straight line from Point A and Point B, including direction.

What is speed?

How quickly an object moves, distance over time

What is velocity?

Speed with direction

What is slope?

The “steepness” of a line, rise (vertical change) over run (horizontal change)

What is a force?

The action that has the ability to change an object’s motion, a push or pull

What is a net force?

The sum of all forces acting on an object

What is the normal force?

The perpendicular force a surface exerts on an object in contact with it (ex: a table exerts the normal force upward on a book laying on it)

What is weight?

A measure of the gravitational force acting on an object.

What is the acceleration due to gravity?

9.81 m/s²

What is friction?

A force that resists motion

What are the 4 types of friction?

Static, sliding, rolling, fluid

What is static friction?

The force between 2 surfaces that aren’t moving

What is sliding (kinetic) friction?

The force opposing the motion of surfaces sliding past each other

What is position?

A variable that tells an object’s specific location relative to an origin, including direction

What is an origin?

The place where an object’s position equals 0

What is magnitude?

The numerical amount of a quantity, the number that goes with a unit

What’s the difference between distance and position?

Distance tells how far an object is from a point without direction, while position tells the object’s exact location relative to the origin, including direction.

What is average speed?

The total distance divided by the total time for a journey

What is instantaneous speed?

The speed of a moving object at any moment (especially over a short distance)

What is the speed/velocity formula?

s = d/t, v = d/t

What is the formula to find distance?

d = s × t

What is the formula to find time?

t = d / s

What is the SI base unit for speed?

Meters per second (m/s)

What is the SI base unit for distance?

meter (m)

What is the SI base unit for velocity?

Meters per second (m/s)

What is the difference between speed and velocity and why is it important?

Speed is how fast something moves. Velocity is speed with direction. Velocity is important because direction matters for figuring out position and timing (like GPS).

How is the direction of a change in position, either backwards or forwards denoted in a velocity measurement?

Backwards is negative (-), forwards is positive (+)

What is the difference between average and instantaneous speed? Provide an example of when you would see both used.

Average speed is total distance ÷ total time over a trip.
Instantaneous speed is how fast you’re going at a specific moment. On a long road trip, you use average speed for the whole drive.
When checking your speed at a stop sign or on the highway, that’s instantaneous speed.

How many meters are in one kilometer?

1000 m

What is rolling friction?

A force resisting the motion that occurs when a wheel, ball, or cylinder rolls freely over a surface

What is fluid friction?

A force resisting the motion between a surface/object and a fluid material: gas or liquid (ex: water or air)

What is air resistance?

A fluid friction that opposes gravity’s motion, causing a terminal velocity

What is Newton’s First Law?

An object will not change its motion because of balanced forces. An object in motion stays in motion with the same velocity and an object at rest stays at rest.

What is Newton’s 2nd Law?

An unbalanced net force causes an object to accelerate, and the acceleration depends on the force and the object's mass.

What is Newton’s 2nd Law equation?

F=ma

What is Newton’s 3rd Law?

Every action has an equal and opposite reaction

What does ∆ mean?

The change of any changeable quantity (ex: A =∆V/T)

What is inertia?

The property of an object that resists changes in its motion

Greater mass → more inertia → takes more force to change its motion

What is terminal velocity and how is it achieved?

The constant speed an object reaches when the force of gravity is balanced by air resistance. It is achieved as the object speeds up and air resistance increases until the forces are balanced.

What is a Position vs. Time graph?

Position on the y-axis, time on the x-axis, can find velocity through position over time (slope)

What is a Distance vs. Time graph?

Distance on the y-axis, time on the x-axis, can find speed through distance over time (slope)

What is a Velocity vs. Time graph?

Velocity on the y-axis, time on the x-axis, can find average acceleration through velocity over time (slope)

What is mass?

The amount of matter in an object

What is a newton?

An SI unit of force, 1 newton = the force needed to make a 1 kg object accelerate (or decelerate) at a rate of 1 m/s²

What is a contact force?

A force transmitted by matter directly touching other matter

What is tension?

A pulling force that acts in a rope, string, or other object and always acts along the direction of the rope

What is a compression?

A “squeeze” or decrease in size

What is an extension?

A “stretch” or increase in size

What is a pound?

The unit of force used in the US equal to 4.448 newtons

What are the 4 fundamental forces in the universe?

Strong nuclear force, electromagnetic force, weak (nuclear) force, gravity

What is a strong nuclear force?

A force that holds the nucleus of an atom together and is very strong but only reaches a very short distance

What is an electromagnetic force?

A force that acts between positive and negative charges and holds atoms together in molecules

What is a weak (nuclear) force?

A force that works inside atoms and causes some kinds of radioactivity

Which of the fundamental forces are important to our daily lives and why?

Gravity: gives us weight and keeps us grounded, keeps the solar system in orbit

Electromagnetism: powers electrical devices, creates contact forces between your atoms and objects’ atoms, holds atoms together (building blocks of matter)

What does it mean to have a positive and negative force that are equal to each other?
(what does the sign (+/-) really mean?)

Forces that have equal magnitude but opposite directions cancel each other out, creating no change in motion. The plus or minus sign represents direction along a coordinate axis, with usually + meaning right/up and - meaning left/down.

What is the difference between a contact force and a force that acts at a distance?

A contact force is created when objects physically touch each other (ex: opening a door), action-at-a-distance forces operate through invisible fields without physical contact (ex: magnets)

What does it mean that the earth is surrounded by a field of force?

It means that any object nearby the earth will be pulled toward the earth’s center and have a force put on it (ex: the moon). This is why the moon and earth have a gravitational pull between them.

How does a spring produce both a push and a pulling force?

A spring pushes back on your hand when you compress it (its coils are forced together) and pulls back when you stretch it (its coils are pulled apart), in both cases, it tries to return to its original length.

How would you measure each of average and instantaneous speed with the CPO equipment?

Average: press both A and B buttons

Instantaneous: choose only A or B

What is the difference between distance and displacement?

Distance measures how far an object is from a point without direction, while displacement measures the object's exact location relative to the origin and includes direction.

What does a constant speed graph look like on a Distance vs. Time graph?

A straight diagonal line with constant slope

What does a constant velocity graph look like on a Velocity vs. Time graph?

A straight horizontal (flat) line

Why is changing direction considered an acceleration like speeding up or slowing down?

Changing direction is considered acceleration because acceleration is any change in velocity, and velocity includes both speed and direction. Therefore, even if speed stays the same, a change in direction changes velocity.

What does accelerated motion look like on a Distance vs. Time graph?

A curved line where the slope is changing

What does accelerated motion look like on a Velocity vs. Time graph?

A straight diagonal line with constant slope

What happens to an object when the net force is balanced?

An object in motion will stay in motion at a constant velocity, and an object at rest will stay at rest.

What happens to an object when the net force is unbalanced?

It will accelerate, or change its speed or direction

How do we add forces, or other vector quantities?

If forces (or other vectors) are acting in the same direction, you add their magnitudes. If the forces on an object are acting in opposite directions, you subtract the forces and the object moves in the direction of the larger force.

What is the difference between mass and weight?

An object’s weight depends on gravitational force and mass and is measured in Newtons. Mass is the amount of matter in an object, and that amount stays constant regardless of location.

Where do we encounter the acceleration due to gravity, and why is it the same for all objects?

It’s encountered near the surface of the Earth. It’s the same because gravity only depends on the mass of the Earth and the distance from its center (which is about the same for everyone, so 9.8 m/s²), not on the mass of the object.

What is a free body diagram, what does it tell us, and what does it not show?

A diagram showing all the forces acting on an object (ex: weight, friction, normal force). It can tell us whether forces are balanced or unbalanced, but it does not show motion, velocity, or acceleration directly.

What is are 2 examples of Newton’s First Law of Motion?

A ball rolling on a flat surface will continue to move until friction (or another unbalanced force) causes it to stop. A book sitting on a table stays there at rest, because the upward normal force and downward gravitational force balance each other out.

What is an example of Newton’s Second Law of Motion?

Pushing a shopping cart: an unbalanced force from your push causes it to accelerate, and the acceleration depends on how hard you push and how heavy the cart is.

Why does Newton’s First Law not distinguish between constant speed and constant rest?

Because they are both natural states, and represent a net force of 0.

What is an example of Newton’s Third Law of Motion?

When you punch a wall, your fist exerts a force on the wall (action), and the wall exerts an equal and opposite force back on your fist (reaction).

What quantity is inertia proportional to, and why?

Mass, because greater mass means greater inertia — the object resists changes in its motion more and takes more force (is harder) to accelerate.

What is the formula for velocity?

V = displacement/time