Motion is all around us. From the cars on the road to the planets in the sky, things are constantly moving. In science, motion is defined as a change in position over time. Understanding the types of motion helps us describe, measure, and predict how objects move in the world.
Force and Motion
Motion is the result of forces acting on objects. Forces can change the speed or direction of an object’s motion. Understanding how forces affect motion is key to understanding how things move, stop, or change direction.
What is a Force?
A force is a push or a pull that can make an object move, stop, or change direction. Forces can be contact forces or non-contact forces:
Contact forces occur when two objects physically interact (e.g., friction, a push or pull).
Non-contact forces can act at a distance, even without touching the object (e.g., gravity, magnetism).
Types of Forces
Gravity
What it is: Gravity is the force that pulls objects toward the center of the Earth (or any other large object, like the Sun or the Moon).
How it affects motion: Gravity gives weight to objects. It also causes things to fall when you drop them. For example, when you jump, gravity pulls you back down.
Real-life example: An apple falling from a tree is an example of gravity in action.
Friction
What it is: Friction is the force that resists the motion of objects sliding or rolling across a surface.
How it affects motion: Friction slows things down or stops them. It depends on the texture of the surfaces in contact. For example, a car tire on a smooth road has less friction than a tire on a rough, gravelly surface.
Real-life example: When you slide a book across a table, friction slows it down and eventually stops it.
Applied Force
What it is: This is the force that you apply to an object, either by pushing or pulling it.
How it affects motion: Applied force can start an object moving, stop it, or change its direction or speed.
Real-life example: When you push a shopping cart, you are applying an applied force.
Normal Force
What it is: The normal force is the force exerted by a surface that supports the weight of an object resting on it.
How it affects motion: It prevents objects from sinking into surfaces. For example, when a book rests on a table, the table exerts an upward normal force that balances the book's weight.
Real-life example: When you sit in a chair, the chair exerts an upward normal force to hold you up.
Air Resistance
What it is: Air resistance is a type of friction that acts on objects moving through the air. It’s also called drag.
How it affects motion: Air resistance slows objects down as they travel through the air. The more streamlined an object, the less air resistance it experiences.
Real-life example: A skydiver experiences air resistance that slows their fall, and a car's speed is affected by air resistance as it moves faster.
You can get a force and motion test and study guide at Teachers Pay Teachers!
You can also get exit tickets at Teachers Pay Teachers!
Don't forget the vocabulary pages at Teachers Pay Teachers!
Types of Motion
Motion doesn’t always look the same—some things move in straight lines, others in circles, and some bounce or spin. Scientists have grouped motion into different types to better understand how objects move. By learning the types of motion, you can start to see patterns and make sense of how things move in your world.
Linear Motion: Linear motion happens when an object moves in a straight line. This can be fast or slow, and the speed may stay the same (uniform motion) or change (non-uniform motion). A car driving on a straight road or a ball rolling across the floor are both examples.
Circular Motion: This type of motion follows a curved or circular path. Think of a Ferris wheel turning, or the Earth orbiting the Sun. In circular motion, the direction is always changing, even if the speed stays the same.
Rotational Motion: Rotational motion means spinning around an axis, which is an invisible line that an object turns around. The Earth rotates once every 24 hours, and so does a spinning basketball or a fan blade.
Periodic Motion: When motion repeats itself in a pattern or cycle, it’s called periodic motion. A swing moving back and forth, or a clock’s pendulum ticking, are great examples. Even your heartbeat is a kind of periodic motion!
Random Motion: In random motion, objects move in unpredictable ways with no clear pattern. For instance, the movement of dust in sunlight or gas particles bouncing in a room shows random motion.
From the steady path of a train to the spinning of a top or the back-and-forth swing of a pendulum, motion comes in many forms. Recognizing different types of motion helps scientists, engineers, and even athletes understand and improve the way things move. Keep observing the world around you—you’ll start to notice motion everywhere!
How to Measure Motion
Understanding how things move is a big part of physics. Scientists measure motion to describe how far something goes, how fast it moves, and how it changes over time. The key ways we measure motion are through distance, speed, velocity, and acceleration.
Distance and Speed
Distance is the total length of the path an object travels. It’s measured in units like meters (m), kilometers (km), or miles.
Speed is how fast an object moves. It tells you the distance something travels in a certain amount of time. The formula is:
Speed = Distance ÷ Time
For example, if a scooter goes 100 meters in 20 seconds, its speed is:
Speed = 100 meters ÷ 20 seconds = 5 meters per second (m/s)
Velocity
Velocity is similar to speed, but it also includes direction. For example, if a car travels north at 60 miles per hour, its velocity is 60 mph north. If it turns and goes east at the same speed, its velocity has changed, even though the speed stayed the same.
Velocity helps scientists describe motion more accurately, especially when direction matters—like in weather patterns, flight paths, or space travel.
Acceleration
Acceleration is a measure of how quickly velocity changes. An object accelerates when it speeds up, slows down, or changes direction. The formula for acceleration is:
Acceleration = Change in Velocity ÷ Time
If a bicycle speeds up from 0 to 10 meters per second in 5 seconds, the acceleration is:
Acceleration = (10 m/s − 0 m/s) ÷ 5 s = 2 m/s²
Acceleration can be positive (speeding up) or negative (slowing down), which is sometimes called deceleration.
By measuring distance, speed, velocity, and acceleration, we can better understand how objects move and predict what they’ll do next!
Projectile Motion
Projectile motion refers to the curved path that an object follows when it is thrown, kicked, or otherwise propelled into the air and is influenced by gravity and air resistance. Unlike straight-line motion, where an object moves in one direction, projectile motion occurs when an object moves both horizontally and vertically at the same time. For example, when you throw a ball, it moves upward and forward at the same time. The upward motion slows down as gravity pulls it back toward the Earth, while the horizontal motion stays constant until air resistance slows it down. The result is a curved trajectory called a parabola. The key thing to remember is that the horizontal and vertical motions are independent of each other, meaning the object will continue moving forward while being pulled down by gravity, creating the characteristic arc. Whether it’s a soccer ball kicked across a field or a rocket launched into space, understanding projectile motion helps explain how objects travel through the air.
Relative Motion
Relative motion refers to how the motion of an object can appear differently depending on the observer’s point of view or reference frame. In other words, the way an object moves can change based on where you are and how fast you are moving. For example, if you are sitting in a car moving at 60 miles per hour and look at another car moving in the same direction at 60 miles per hour, it may appear that the other car is not moving at all, even though it is. However, if you were to look at the car from outside on the road, you would see both cars moving at 60 miles per hour. This is because motion is always measured relative to something else. Whether you’re in a moving car, on a train, or standing still, the way you observe motion depends on your perspective, making relative motion an important concept in understanding how we perceive the movement of objects around us.
Motion in Space
Motion in space is unique because there is very little resistance, such as air or friction, to slow objects down. In space, once an object is set in motion, it continues to move in the same direction at a constant speed unless a force acts upon it. This is due to the absence of friction, which on Earth often slows down moving objects. For example, when a rocket is launched, it continues to travel through space at the same speed and direction until it encounters another force, like gravity from a planet or moon, which can change its path. Objects in space, like planets, moons, and satellites, move in elliptical orbits due to the gravitational pull of larger celestial bodies. Unlike on Earth, where gravity pulls objects toward the ground, in space, gravity keeps celestial objects in constant motion around each other, ensuring that planets stay in orbit around the Sun and moons around their planets. This consistent motion is a fundamental aspect of how objects behave in the vacuum of space.
Planetary Motion
Long ago, people believed that Earth was at the center of the universe and that the Sun, Moon, and planets all moved around it. This idea, called the geocentric model, was supported by early astronomers like Ptolemy. But as scientists learned more and began to use careful observations and mathematics, their understanding of planetary motion changed dramatically.
In the 1500s, a Polish astronomer named Nicolaus Copernicus proposed a bold new idea: the Sun is at the center, and the planets, including Earth, orbit around it. This became known as the heliocentric model. At first, many people didn’t believe him because it went against what they had always been taught.
Later, Johannes Kepler, a German scientist, studied data collected by another astronomer, Tycho Brahe, and discovered that planets don’t move in perfect circles. Instead, he found that planets travel in elliptical orbits, which are oval-shaped. Kepler created three laws of planetary motion that accurately described how planets move around the Sun.
Then came Galileo Galilei, who used one of the first telescopes to observe the sky. He saw moons orbiting Jupiter and phases of Venus, which supported the heliocentric model. Finally, in the 1600s, Isaac Newton explained why planets move the way they do by discovering the law of gravity, showing that the Sun’s gravity keeps planets in orbit.
These scientists changed the way we see the universe. Their discoveries about planetary motion helped launch the modern science of astronomy and showed that learning through careful observation and testing could reveal the true nature of the cosmos.
Force and Motion Flashcards
You can get force and motion printable flashcards at Teachers Pay Teachers. You can also see them here for free!
Middle School Science
