Eighth Grade Physics of Forces, Motion and Energy

Getting Started

A comprehensive course that continues the science adventure in physics under Newton’s work on the three laws of motion.

(Note: If you’re wanting a more in-depth physics course (not just lab experiments but additional content including calculations), then you’ll want to visit our Physics Course in the Advanced section. You do not need to complete the content on this page in order to do the Advanced Physics Course.)

Students get a crash-course in projectile motion as they build g-force accelerometers, float hovercraft on both land and water, build a rocket car, and measure the Earth’s magnetic pulse. For advanced students, you'll find a complete course in thermal energy here to augment the topics covered in this section.

Here are the scientific concepts:

A force is a push or a pull. A force has both direction and magnitude.
When an object is subject to two or more forces at once, the effect is the cumulative effect of all the forces.
When the forces on an object are balanced, the motion of the object does not change.
Newton's First Law of Motion states that an object will remain at rest or keep moving in a straight line at the same speed unless acted upon by an unbalanced force. This is called inertia, the tendency of objects to resist changes in their motion.
Forces that act at a distance (electric and magnetic) can be explained by fields that extend through space and can be mapped by their effect on a test object (a ball, a charged object, or a magnet, respectively).
Electric and magnetic (electromagnetic) forces can be attractive or repulsive, and their sizes depend on the magnitudes of the charges, currents, or magnetic strengths involved and on the distances between the interacting objects.
Gravitational forces are always attractive. There is a gravitational force between any two masses, but it is very small except when one or both of the objects have large mass—e.g., Earth and the sun.
The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change.
The greater the mass of the object, the greater the force needed to achieve the same change in motion.
For any given object, a larger force causes a larger change in motion.
Motion energy is called kinetic energy, and is proportional to the mass of the moving object and grows with the square of the speed.
When the motion energy of an object changes, energy is transferred to or from the object.
A system of objects may also contain stored (potential) energy depending on its location.
Gravitational potential energy is the amount of energy something has due to its height above the ground.
The higher the object is, the more gravitational potential energy it has.
For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in the opposite direction.
The velocity of an object is the change of its position over a given about of time.
Velocity is a vector, which means it was both direction and speed.
Acceleration is a change in velocity, which can be changes in speed, direction, or both.
Average speed is the total distance traveled divided by the total time elapsed. The speed of an object along the path traveled can vary.

By the end of the labs in this unit, students will be able to:

Differentiate observation from inference (interpretation) and know scientists’ explanations come partly from what they observe and partly from how they interpret their observations.
Measure and estimate the length and volume of objects.
Formulate and justify predictions based on cause-and-effect relationships.
Conduct multiple trials to test a prediction and draw conclusions about the relationships between predictions and results.
Construct and interpret graphs from measurements.
Follow a set of written instructions for a scientific investigation.

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Physics Calculations Videos

These videos are taken from the first few lessons in high school section for Physics. If you feel ready to jump into the actual high school Physics course, go here.

	Detecting the Gravitational Field Ok, sort of a silly experiment I admit. But here's what we're going for - there is an invisible force acting on you and the ball. As you will see in later lessons, things don’t change the way they are moving unless a force acts on them. When you jump, the force that we call gravity pulled you back to Earth.
	Detecting the Magnetic Field Remember, there are four different kinds of forces: strong nuclear force, electromagnetism, weak nuclear force, and gravity. There are also four basic force fields that you come into contact with all the time.
	The Electromagnetic Field The electromagnetic field is a bit strange. It is caused by either a magnetic field or an electric field moving. If a magnetic field moves, it creates an electric field. If an electric field moves, it creates a magnetic field.
	Detecting the Electric Field You are actually fairly familiar with electric fields too, but you may not know it. Have you ever rubbed your feet against the floor and then shocked your brother or sister?
	Flying Paper Clip Have you ever been close to something that smells bad? Have you noticed that the farther you get from that something, the less it smells, and the closer you get, the more it smells? Well forces sort of work in the same way.
	Force-full Cereal Did you know that your cereal may be magnetic? Depending on the brand of cereal you enjoy in the morning, you'll be able to see the magnetic effects right in your bowl. You don't have to eat this experiment when you're done
	Net Forces It is very rare, especially on Earth, to have an object that is experiencing force from only one direction. A bicycle rider has the force of air friction pushing against him. He has to fight against the friction between the gears and the wheels.
	A Weighty Issue This lesson may give you a sinking sensation but don’t worry about it. It’s only because we’re talking about gravity. You can’t go anywhere without gravity. Even though we deal with gravity on a constant basis
	Forever Falling If I pitch a ball toward the sunset at the exact same instant that I drop another one from my other hand, which one reaches the ground first? For this experiment, you need
	Chicken and the Clam Next time you watch a drag race, notice the wheels. Are they solid metal discs, or do they have holes drilled through the rims?
	TaaDaaaaa!!! Ever wonder how magicians work their magic? This experiment is worthy of the stage with a little bit of practice on your end.
	Look Out Below! If you jump out of an airplane, how fast would you fall? What's the greatest speed you would reach? Let's practice figuring it out without jumping out of a plane.
	Circular Motion This experiment is for advanced students. Circular motion is a little different from straight-line motion in a few different ways. Objects that move in circles are roller coasters in a loop, satellites in orbit, DVDs spinning in a player, kids on a merry go round, solar systems rotating in the galaxy, making a left turn … Continue reading "Circular Motion"
	Driveway Races This experiment is one of my favorites in this acceleration series, because it clearly shows you what acceleration looks like. The materials you need is are:
	Gyro Wheel Gyroscopes defy human intuition, common sense, and even appear to defy gravity. You'll find them in aircraft navigation instruments, games of Ultimate Frisbee, fast bicycles, street motorcycles
	Downhill Race Newton’s Second Law is one of the toughest of the laws to understand but it is very powerful. In its mathematical form, it is so simple, it’s elegant.
	G-Force A common misconception in science is that centrifugal and centripetal force (or acceleration) are the same thing. These two terms constantly throw students into frenzy, mostly because there is no clear definition in most textbooks.
	Balloon Racers We're going to experiment with Newton's Third law by blowing up balloons and letting them rocket, race, and zoom all over the place. When you first blow up a balloon, you're pressurizing the inside of the balloon by adding more air (from your lungs) into the balloon.
	Homemade Pulleys These homemade pulleys work great as long as they glide freely over the coat hanger wire (meaning that if you give them a spin, they keep spinning for a few more seconds). You can adjust the amount of friction in the pulley by adjusting the where the metal wire bends after it emerges from the pulley.
	Ball Bounce When you toss down a ball, gravity pulls on the ball as it falls (creating kinetic energy) until it smacks the pavement, converting it back to potential energy as it bounces up again. This cycles between kinetic and potential energy as long as the ball continues to bounce.
	Elastic Potential Energy There are many different kinds of potential energy. We've already worked with gravitational potential energy, so let's take a look at elastic potential energy.
	Pendulums This is a very simple yet powerful demonstration that shows how potential energy and kinetic energy transfer from one to the other and back again, over and over. Once you wrap your head around this concept, you'll be well on your way to designing world-class roller coasters.
	Catapults When you drop a ball, it falls 16 feet the first second you release it. If you throw the ball horizontally, it will also fall 16 feet in the first second, even though it is moving horizontally… it moves both away from you and down toward the ground.
	Potato Cannon This experiment is for kids Grades 9-12.There are several different ways of throwing objects. This is the only potato cannon we've found that does NOT use explosives, so you can be assured your kid will still have their face attached at the end of the day.
	P-Shooters This is a simple, fun, and sneaky way of throwing tiny objects. It's from one of our spy-kit projects. Just remember, keep it under-cover. Here's what you need:
	Bobsleds Bobsleds use the low-friction surface of ice to coast downhill at ridiculous speeds. You start at the top of a high hill (with loads of potential energy) then slide down a icy hill til you transform all that potential energy into kinetic energy.
	Roller Coasters We're going to build monster roller coasters in your house using just a couple of simple materials. You might have heard how energy cannot be created or destroyed
	Go Go GO!! This is a nit-picky experiment that focuses on the energy transfer of rolling cars. You'll be placing objects and moving them about to gather information about the potential and kinetic energy.
	Newton’s First Law of Motion First Law of Motion: Objects in motion tend to stay in motion unless acted upon by an external force. Force is a push or a pull, like pulling a wagon or pushing a car. Gravity is a force that attracts things to one another. Gravity accelerates all things equally. Which means all things speed up … Continue reading "Newton’s First Law of Motion"
	Newton’s Second Law of Motion Second Law of Motion: Momentum is conserved. Momentum can be defined as mass in motion. Something must be moving to have momentum. Momentum is how hard it is to get something to stop or to change directions. A moving train has a whole lot of momentum. A moving ping pong ball does not. You can … Continue reading "Newton’s Second Law of Motion"
	Newton’s Third Law of Motion Third Law of Motion: For every action, there is an equal and opposite reaction. Force is a push or a pull, like pulling a wagon or pushing a car. Gravity is a force that attracts things to one another. Weight is a measure of how much gravity is pulling on an object. Gravity accelerates all … Continue reading "Newton’s Third Law of Motion"
	Maxwell’s First Equation Maxwell’s First Equation: Like charges repel; opposites attract. The proton has a positive charge, the neutron has no charge (neutron, neutral get it?) and the electron has a negative charge. These charges repel and attract one another kind of like magnets repel or attract. Like charges repel (push away) one another and unlike charges attract … Continue reading "Maxwell’s First Equation"
	Maxwell’s Second Equation Maxwell’s Second Equation: All magnets have two poles. Magnets are called dipolar which means they have two poles. The two poles of a magnet are called north and south poles. The magnetic field comes from a north pole and goes to a south pole. Opposite poles will attract one another. Like poles will repel one … Continue reading "Maxwell’s Second Equation"
	Maxwell’s Third Equation Maxwell’s Third Equation: Invisible magnetic fields exert forces on magnets AND invisible electrical fields exert forces on objects. A field is an area around a electrical, magnetic or gravitational source that will create a force on another electrical, magnetic or gravitational source that comes within the reach of the field. In fields, the closer something … Continue reading "Maxwell’s Third Equation"
	Maxwell’s Fourth Equation Maxwell’s Fourth Equation: Moving electrical charges (fields) generate magnetic fields AND changing magnetic fields generate electrical fields (electricity). We're going to do a couple of experiments to illustrate both of these concepts. Magnetic fields are created by electrons moving in the same direction. A magnetic field must come from a north pole of a magnet … Continue reading "Maxwell’s Fourth Equation"

Getting Started

Here are the scientific concepts:

By the end of the labs in this unit, students will be able to:

Physics Calculations Videos

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