General Physics 1

Motion

Motion means an object's position changes relative to a reference point over time.

Position

Position tells you where an object is located relative to a chosen reference point.

Reference Point

A reference point is the location or object used to determine whether something has changed position.

Distance

Distance is the total amount of ground or path an object travels.

Displacement

Displacement describes how an object's final position compares with its starting position.

Distance vs. Displacement

Distance describes the entire path traveled, while displacement describes the change from starting position to ending position.

Speed

Speed describes how fast an object is moving.

Velocity

Velocity describes both how fast an object is moving and the direction in which it moves.

Speed vs. Velocity

Speed tells you how fast something moves; velocity tells you how fast and in what direction.

Acceleration

Acceleration means velocity is changing. The change can involve speed, direction, or both.

Velocity and Acceleration

Velocity describes an object's current motion, while acceleration describes how that motion is changing.

Speeding Up

An object speeds up when its acceleration acts in the same direction as its velocity.

Slowing Down

An object slows down when its acceleration acts opposite to its velocity.

Zero Acceleration

Zero acceleration means the object's velocity is not changing.

Zero Acceleration and Motion

An object can have zero acceleration while moving; it simply continues with constant velocity.

Constant Velocity

Constant velocity means the object's speed and direction remain unchanged.

Changing Direction

An object can accelerate even when its speed stays the same because changing direction changes velocity.

Scalar

A scalar quantity has magnitude only.

Vector

A vector quantity has magnitude and direction.

Scalar Examples

Distance, speed, and mass are scalar quantities.

Vector Examples

Displacement, velocity, acceleration, and force are vector quantities.

Direction in Physics

Direction tells you which way a vector quantity points and is often described using words such as north, south, east, west, upward, or downward.

Positive and Negative Directions

Positive and negative signs can represent opposite directions chosen in a coordinate system.

Newton's First Law

An object tends to maintain its current state of motion unless a net force changes that motion.

Inertia

Inertia is an object's tendency to resist changes in its motion.

What Changes Motion

A net force causes an object's velocity to change, meaning it can speed up, slow down, or change direction.

Balanced Forces

When forces balance, there is no net force and the object's motion does not change.

Unbalanced Forces

When forces do not balance, there is a net force and the object's velocity changes.

Net Force

The net force is the combined effect of all forces acting on an object.

Newton's Second Law

Newton's Second Law explains that an object's acceleration depends on the net force acting on it and its mass.

Force and Acceleration

A greater net force produces greater acceleration when mass stays the same.

Mass and Acceleration

For the same net force, a more massive object accelerates less than a less massive object.

Newton's Third Law

When one object exerts a force on another object, the second object exerts an equal and opposite force back.

Interaction

Newton's Third Law describes forces as interactions between two objects; the force from one object is paired with a force from the other.

Action-Reaction Pair

An action-reaction pair consists of two equal and opposite forces produced by the interaction of two objects.

Truck and Car Collision

During a collision, the truck and car exert equal forces on each other, even though their accelerations may be different.

Hammer and Nail Interaction

The hammer pushes the nail, and the nail pushes back on the hammer; these forces are an interaction between two objects.

Mass

Mass describes how much matter an object contains and also relates to how difficult it is to change the object's motion.

Weight

Weight is the gravitational force acting on an object.

Mass vs. Weight

Mass describes the amount of matter in an object, while weight describes the gravitational pull acting on that object.

Gravity

Gravity is the attractive force associated with massive objects and causes objects near Earth's surface to accelerate downward.

Gravitational Acceleration

Near Earth's surface, gravity causes objects to accelerate downward at approximately 9.8 m/s².

Free Fall

Free fall is motion where gravity is the force responsible for the object's acceleration, with air resistance ignored.

Mass and Free Fall

When air resistance is ignored, objects of different masses have the same gravitational acceleration.

Vacuum

A vacuum contains no air, so there is no air resistance affecting falling objects.

Air Resistance

Air resistance is a force from air that can affect an object's motion as it moves through the atmosphere.

Object Thrown Upward

When an object is thrown upward, it moves upward while gravity continuously accelerates it downward.

Highest Point of Vertical Motion

At the highest point, an upward-moving object momentarily has no upward velocity before beginning to move downward.

Gravity at the Highest Point

Gravity continues acting downward even when the object reaches its highest point.

Projectile

A projectile is an object moving through the air under the influence of gravity, with air resistance commonly ignored in basic analysis.

Projectile Components

Projectile motion can be understood by considering horizontal motion and vertical motion separately.

Horizontal Projectile Motion

Without air resistance, horizontal motion continues at constant velocity because there is no horizontal acceleration.

Vertical Projectile Motion

Vertical projectile motion is affected by gravity, which continuously accelerates the object downward.

Projectile at the Apex

At the highest point of an angled projectile, its vertical motion temporarily stops while its horizontal motion continues.

Dropped Object vs. Horizontally Launched Object

If two objects begin at the same height with the same initial vertical velocity, their vertical falling motion is the same when air resistance is ignored.

Normal Force

The normal force is the support force a surface exerts on an object, acting perpendicular to the surface.

Book on a Table

A stationary book on a horizontal table is supported upward by the table while gravity pulls it downward.

Balanced Book on Table

When a book is stationary on a level table and no other vertical forces act, the upward support from the table balances the downward gravitational force.

Normal Force and Surfaces

The normal force depends on the situation and the orientation of the surface; it is not automatically the same in every situation.

Ramp Forces

On a ramp, gravity can be separated into components parallel and perpendicular to the surface, helping determine the object's motion and normal force.

Equilibrium

Equilibrium means the forces acting on an object are balanced so there is no translational acceleration.

Translational Equilibrium

An object is in translational equilibrium when its net force is zero.

Stationary Equilibrium

An object can be in equilibrium while remaining at rest.

Moving Equilibrium

An object can also be in equilibrium while moving at constant velocity because its velocity is not changing.

Rotational Equilibrium

Rotational equilibrium means the forces produce no net rotational effect, so the object's rotational motion does not change.

Complete Equilibrium

For complete mechanical equilibrium, both translational forces and rotational effects must be balanced.

Torque

Torque describes the tendency of a force to cause an object to rotate.

Elevator Motion

To analyze an elevator problem, focus on whether the elevator's velocity is changing and determine the direction of its acceleration.

Scale

A bathroom scale measures the force the scale exerts on the person standing on it.

Normal Force on a Person

The scale pushes upward on the person; this upward support force is the normal force.

Apparent Weight

Apparent weight is the amount of support force a person experiences or the force indicated by a scale.

Actual Weight vs. Apparent Weight

Actual weight comes from gravity, while apparent weight depends on the support force acting on the person.

Elevator Accelerating Upward

When the elevator accelerates upward, the scale must provide more upward support, so the person feels heavier.

Elevator Accelerating Downward

When the elevator accelerates downward, the scale provides less upward support, so the person feels lighter.

Elevator at Constant Velocity

If an elevator moves at constant velocity, its acceleration is zero and the person's scale reading is normal.

Elevator Moving Upward and Speeding Up

The elevator's velocity is upward and increasing, so its acceleration is upward and the person feels heavier.

Elevator Moving Upward and Slowing Down

The elevator's velocity is upward but decreasing, so its acceleration is downward and the person feels lighter.

Elevator Moving Downward and Speeding Up

The elevator's velocity is downward and increasing, so its acceleration is downward and the person feels lighter.

Elevator Moving Downward and Slowing Down

The elevator's velocity is downward but decreasing, so its acceleration is upward and the person feels heavier.

Free-Falling Elevator

In a freely falling elevator, the passenger and elevator accelerate downward together, so the passenger is no longer supported by the floor in the usual way.

Weightlessness

Weightlessness in free fall means the support force is essentially absent; it does not mean gravity has disappeared.

Motion in Deep Space

In an environment with no significant opposing forces, an object that has been set into motion can continue moving without needing a continuous push.

Thruster and Motion

A thruster changes an object's motion by applying a force. Once the force stops, the object keeps its current velocity if no other net force acts.

Newton's First Law in Space

An object continuing to move after a brief push in empty space is an example of inertia.

Velocity-Time Graph

A velocity-time graph shows how velocity changes as time passes.

Slope of a Velocity-Time Graph

The slope of a velocity-time graph represents acceleration because it shows how quickly velocity changes.

Horizontal Velocity-Time Graph

A horizontal velocity-time graph means velocity remains constant, so there is no acceleration.

Velocity-Time Graph Above Zero

A horizontal line above the time axis represents constant motion in the positive direction.

Velocity-Time Graph Below Zero

A horizontal line below the time axis represents constant motion in the negative direction.

Velocity-Time Graph on Zero

If the graph lies on the time axis, the velocity is zero and the object is at rest.

Positive Slope on a v-t Graph

A positive slope means velocity is increasing in the positive direction.

Negative Slope on a v-t Graph

A negative slope means velocity is decreasing with time.

How to Read Motion Problems

Identify what is happening to the object's position, velocity, and acceleration before deciding which physical principle applies.

How to Analyze Forces

Identify every force acting on the object, determine their directions, and decide whether they balance.

How to Analyze Acceleration

First determine whether velocity is changing. If it is changing, determine whether the object is speeding up, slowing down, or changing direction.

How to Analyze Direction

Choose a reference direction and use positive and negative signs consistently to represent opposite directions.

How to Analyze Equilibrium

Ask whether the forces balance and whether the object's motion is changing. Balanced forces mean no translational acceleration.

How to Analyze Falling Objects

Ignore mass as a reason for different falling acceleration when air resistance is absent; focus on gravity and the vertical motion.

How to Analyze Projectile Motion

Separate the horizontal and vertical parts of the motion. Gravity affects the vertical part while horizontal velocity continues independently when air resistance is ignored.

How to Analyze Elevator Problems

Determine the elevator's acceleration from whether its velocity is increasing or decreasing, then relate the acceleration to how much support the scale must provide.