How To Teach Physics With Pictures

Mention that physics is one of the oldest academic fields and stems from humanity’s basic need to understand how the universe works. You could also bring up the discipline’s impacts on human life. Explain that discoveries in physics led to feats from the smartphones in their pockets to nuclear technology. Connecting physics to basic human drives and discussing its impacts on life can help your students relate to the discipline and its aims.

Remind your students that a hypothesis attempts to answer the question about what’s been observed. For instance, a person might observe that things fall to the ground, and wonder if all objects fall at the same rate. They hypothesize that objects fall at different rates, and conduct experiments to test their claim. Suppose that, at first, their hypothesis in this example seems to be correct. They drop a feather and a rock, and see the objects fall at different rates. However, when they account for air resistance, they find that all objects on Earth fall at a rate of about 9. 8 m/s2. Explain that physicists use mathematical expressions to express their hypotheses. They use math to hypothesize about an object’s motion or a fundamental force.

The meter (m), which measures length. The kilogram (kg), or the unit of mass. The second (s), which measures duration. The ampere (A), which measures electrical current. The kelvin (K), the unit for temperature. The mole (mol), which measures the amount of substance, or the number of elementary particles in an object. The candela (cd), which measures the intensity of light.

Tell your students that they’ll learn a variety of equations that include different variables, or letters that stand for measured quantities. They’ll know some variables, and need to solve for others. The equations express mathematical relationships, which allows them to use the values they know to find an unknown variable. The formula for speed is nice and simple, so it’s a great way to introduce physics equations. Write “s = d/t” on the board, and say, “This is the formula to find speed. If I know d, or distance, and t, or time, I can divide d by t to find s. ” Then continue, “I can rework this equation depending on my known and unknown variables. Suppose I know the variables s and t, but need to find d. ” Write “s = d/t,” on the board then “2 = d/5” under it. Say, “Speed, distance, and time have a relationship. If I multiply 2, or time, by 5, or speed, I can find distance, or 10. If I travel at 2 meters per second for 5 seconds, I’ve traveled 10 meters. ”

Providing clear examples as you introduce terms not only helps your students understand what you’re saying in the moment, it will help them relate more complex examples back to these concepts as they get further into your course.

Define scalars as measurements that describe a magnitude alone, such as an object’s speed or a distance. Offer examples of scalar quantities, such as a distance of 20 m, a speed of 10 m/s, and a mass of 100 g. Clarify that these numbers are scalars because they don’t give information about direction. Explain that, in contrast, vectors describe both magnitude and direction, such as a velocity of 40 m/s north, an acceleration of 9. 8 m/s2 downward, or a displacement of 25 m west. Try rolling a toy car forward, and say, “This car is moving 5 m/s west. Is this a vector or a scalar?” Then draw 2 rectangles on the board, connect them with an arrow labeled “10 m,” and say, “This brick has moved 10 m. We don’t know the direction in which it has moved. Is this a vector or scalar?”

For a helpful visual example, take a meter-sized step as you count out 1 second. Say, “I traveled 1 meter in 1 second. My speed was 1 meter per second. ” Then move a toy car and say, “Speed equals distance over, or divided by, time. Suppose this car has traveled 2 meters in 1 second. Let’s fill in the formula s = d/t, so s = 2 m/1 s. The car’s speed is 2 m/s. If it traveled 120 m in 3 seconds, s = 120 m/3 s, or 40 m/s. ” Remind students that they can flip the formula around to find other missing variables. If they know the car’s constant speed is 2 m/s, and it’s been driving for 130 seconds, they can use the formula d = st to find the distance it traveled: d = (2)(130) = 260 m.

If a car’s initial velocity is 4 m/s west, and it accelerates at 3 m/s/s in the same direction for 5 s, its final velocity is (4) + (3)(5), or 19 m/s w. Emphasize that speed is distance traveled over time, but velocity is the rate at which an object changes its position. For example, if you walked forward 2 meters at a speed of 1 m/s, then back to the same spot at the same speed, your position didn’t change. Since your position didn’t change in this motion, your velocity is 0 m/s.

For instance, if a car accelerates from 5 m/s to 8 m/s in 3 s, its average acceleration equals (8-5) / (3), or 1 m/s2. Mention that, on Earth, the acceleration of gravity is 9. 8 m/s2. Explain that m/s2 means meters per second per second. This means a falling object accelerates (or changes its initial velocity) 9. 8 m/s each second: 9. 8 m/s at 1 second, 19. 6 m/s at 2 seconds, 29. 4 m/s at 3 seconds, and so on.

To help your students see how displacement works, move your toy car and say, “This car’s velocity is 5 m/s forward, and it accelerates at 2 m/s/s (meters per second per second, or m/s2) over a duration of 3 s. ” Write the equation on the board: d = (5)(3) + ½(2)(3)2, or 15 + 9. Displacement equals 24 m forward.

Say, “Two-dimensional motion, or motion in 2 directions, involves 2 independent parts, which are called ‘components. ’ Suppose I pull my dog’s leash upward and backward (draw a diagonal line on the graph to represent the leash). This vector is made of 2 parts, or the upward component and a backward component. These parts are separate and independent from each other. ” Now draw a cannon on the edge of a cliff. Draw a cannonball launched horizontally at 20 m/s, and add dots representing the ball as it moves forward and downward in a curved line. Tell your students that the vertical and horizontal components are independent motions. Say, “On Earth, gravity causes objects to fall at a rate of about 9. 8 m/s. This means the cannonball’s vertical velocity, or y increases by 9. 8 m/s downward each second. At 1 second, vy = 9. 8 m/s downward, at 2 seconds vy = 19. 6 m/s down, and at 3 seconds it’s moving 29. 4 m/s downward. If there are no horizontal forces acting on the cannonball, its horizontal velocity, or vx remains constant at 20 m/s. ”

Write “60°” at the angle between the diagonal line, or the vector, and the rectangle’s lower horizontal line. Explain that, “This angle can help us find the cannonball’s horizontal velocity (point to the bottom of the rectangle) and vertical velocity (point to the right side of the rectangle). ” Show your students that cosine and sine are ratios between a right triangle’s angles and sides. Point to the 60° angle and say, “The ratios between this angle, the diagonal line, or the hypotenuse, and the horizontal and vertical lines can help us find unknown variables. We know the velocity, or the diagonal line is 50 m/s at 60° above the horizontal. To find the horizontal line, or vx, we’ll multiply the diagonal line by the cosine of the angle. This means vx = (50 m/s)(cos60°). The cosine of 60° is 0. 5, so vx = 25 m/s forward. ” Next, explain how to find the vertical component. Point to the vertical line and say, “To find this value, or the upward component of the object’s motion, we’ll multiply the sine of the 60° angle by the object’s velocity: vy = (50 m/s)(sin60°), or about 43 m/s upward. ”

The first law of motion, or the law of inertia, states that any object in motion will stay in motion at the same speed and same direction unless another force acts on it. Say, “Imagine a hockey puck rolling over ice. The force of friction slows the puck, so it doesn’t travel forever. If the ice were perfectly frictionless, the puck would stay in motion. ” Newton’s second law states that the force acting on an object determines its change in momentum. This law gives us the equation F = m / a, which we can use to find the magnitude of a force. F is force (measured in newtons), m is the object’s mass, and a is its acceleration. Roll your toy car forward, then give it additional pushes forward and backward. Tell the class that second law explains how the backward and forward forces change the car’s motion. The third law states that every action has an equal and opposite reaction. Say, “If a road exerts frictional force on a car’s tires, the car’s tires also exert friction on the road. When you sit on a chair, you exert a downward force on it, and it exerts an upward force on you. ”

Write the formula W = Fd cosθ on the board, where W is work, F is force, d is displacement, and cosθ is the cosine of the angle between the force direction and the object’s direction of motion. Mention that the unit of measurement for work is joules, which is 1 newton of force exerted over 1 meter, or 1 N multiplied by 1 m. Note that if the direction of the force and the direction of the object’s motion are the same, the angle between them is 0°, and the cosine of 0 is 1. To offer an example, say, “Suppose a person is pushing a lawn mower at a downward angle of 60° with a force of 900 N, and they’ve pushed the lawn mower 30 m. To calculate work, enter the variables into the equation (write them on the board): W = (900)(30)(cos60°). The cosine of 60° is 0. 5, so W = (27,000)(0. 5), or 13,500 J. ”

As you write the formula on the board, say, “To calculate kinetic energy, which is measured in joules, use the formula KE = ½mv2. The m stands for mass and v is velocity. Suppose a bowling ball that weighs 5 kg is rolling at 3 m/s. Plug the variables into the equation to find its kinetic energy: KE = ½(5)(3)2, or 16 J. ”

To calculate elastic potential energy, or energy stored in a spring, write the formula U = ½kx2 on the board. Explain that k refers to the spring’s stiffness, or its spring constant, and x is how far it’s been stretched. For example, if a spring with a spring constant of 10 N/m has been stretched 1 m, its potential energy is ½(10)(1)2, or 25 J. To find the gravitational potential energy (on Earth), show them the formula U = mgh, where m is the object’s mass, g is the Earth’s gravitational constant (9. 8 m/s2), and h is the object’s height. Tell them, “Suppose a drone weighs 2 kg and is flying at a height of 100 m. Its gravitational potential energy equals (2)(9. 8)(100), or 1,960 J. ”

Tell your students, “Outside of the vacuum container, the feather doesn’t fall more slowly because it weighs less than the rock. The feather has more surface area and collides with particles of air. This is called air resistance, and if you remove the air, the objects fall at the same rate. ” Since it’s so counterintuitive, this is a good introductory experiment, especially for younger students. It can help them see how many variables are involved in motion and force.

Before throwing the balls and marking distances, ask students to make predictions about how balls thrown at each angle will travel. They can answer verbally or write their answers on a handout. Have your students closely observe the balls as they’re thrown. Showing slow-motion videos of balls being thrown could also be helpful. Point out the curved shape of the balls’ trajectories, and label this term “parabola. ” Explain, “Balls thrown at medium angles usually travel the farthest. Gravity pulls balls thrown at shallow angles down sooner, so they don’t have time to travel far. Balls thrown higher spend more energy resisting gravity than they do traveling forward. ” Throw the balls as hard as you can so the throwing force remains relatively consistent. For a bonus lesson, use various types of balls, such baseballs and wiffle balls, to explore how shape, weight, and drag affect the results.

Measure how far a push sends the skater over rough, bumpy pavement. Note how far a push of the same force sends the skater over a smooth surface. Give the skater a gentle push or pull as they’re already moving forward. Tell your class, “Friction slows down the skater’s motion, even if the same force was applied. When they’re moving forward, a push forward increases their forward motion. ” Make sure the skater wears a helmet and pads, and instruct your students to pull or push gently and slowly. A spotter can help the skater stay on their feet. If you’re worried about accidental injuries, use a skateboard without a rider or a cart. For a bonus lesson, have the skater carry textbooks or place objects in the cart. Point out that, as Newton’s second law states, the same force applied to objects with less mass makes them travel farther

Consider making a protective case of your own with ample lightweight cushioning around the egg and a well-constructed parachute, just in case none of the groups create a successful design. Point how how a parachute lowers the rate of descent, and explain that the egg converts potential energy to kinetic energy as it falls. Write out the formula for kinetic energy (KE = ½mv2) and say, “A smaller mass and lower velocity means lower kinetic energy. The parachute lowers the egg’s velocity, and lightweight cushioning protects the egg, but keeps the overall mass low. ”