## Lesson Plan

Physics on the Playground

Sliding, climbing, swinging — playgrounds are a great place to observe physical forces, such as gravity, momentum, and friction.

- Grades: 3–5

Invite students outdoors to take a closer look at the science behind the fun with these hands-on activities. Encourage them to predict, observe, and draw conclusions along the way.

If you want students to record their predictions and observations along the way, provide notebooks or paper and writing implements for each student before beginning the activities.

### Swinging Forces

**Materials Needed:**

- Access to at least one swing
- Plain, white paper, one piece per student
- Pencils, pens, or markers

**Science Concept**: What makes a swing swing? When someone pushes you on the swing, they increase your kinetic energy. The push acts as an external force that propels you to swing forward. Another way to get height on a swing is to simultaneously pump your legs and rock forward and back. Pumping your legs increases your potential energy, and leaning forward raises your center of gravity slightly — all of which get you to swing higher and higher. Meanwhile, the pull of gravity, which draws all objects to Earth, works to pull the swing toward the ground on its downward trajectory.

**Try This**: After explaining these concepts, ask a student volunteer to sit on a swing, without pumping, and another student to give him or her a few solid pushes. Have the rest of the class stand safely to one side and observe.

**Questions**: Ask students to watch the swing action at three key points: the two peaks of the motion and the lowest point. Next, challenge them to draw a diagram of the three points and identify at each point the force that controls the movement. Kinetic energy is the middle part of the swinging, when the swing is approaching its peak on either side. Potential energy is the peak of the swinging on either side, when the swing is temporarily still. When the swing falls from either peak to the ground, the force of gravity is acting upon it.

### Slip Sliding Away: Friction Comparison

**Materials Needed:**

- Access to at least one slide
- Assorted materials to slide on, such as carpet scraps, cardboard, plastic bags, different fabrics, and rubber mats

**Science Concept**: Without gravity pulling downward and powering the ride, slides really wouldn’t slide. But another force is usually working against gravity to slow down the fun: friction.

**Try This**: Challenge students to minimize friction for the fastest, smoothest ride down the slide. Provide a variety of materials for them to sit on, such as carpet scraps, cardboard, plastic bags, fabrics, and a rubber mat.

**Questions**: Ask students to predict which materials, including their own clothing, will create the least amount of friction. Next, ask pairs to test the materials by having one student slide down and another time the ride until the slider´s feet touch the ground. Which of the materials creates the fastest ride? Why?

### Air Resistance Test

**Materials Needed:**

- Access to climbing equipment or chairs (for students to stand on)
- Plain, white paper, one piece per student and two pieces for the demonstration

**Science Concept:** Air resistance — the push of air against a moving object — can have a surprising effect on gravity.

**Try This**: Tell students that a bowling ball and a feather will fall at the same speed — if nothing is in the way of their fall. What does get in their way? Invisible air! Hold up two identical pieces of paper, and crumple one into a ball.

**Questions**: Ask students to predict which one will fall faster. Then have student pairs investigate by dropping twice pieces of paper — one flat and one crumpled — at the same time from a high place on the playground. Ask students: If the pieces weigh the same, why does one fall faster? The answer is air resistance: more air pushes back against the larger surface area of the flat piece, slowing its fall.

### Stronger Than Gravity

**Materials Needed:**

- Tennis ball
- Medium-sized bucket

**Science Concept**: Is there any force that can defy gravity? According to Newton’s First Law of Motion, an object at rest stays at rest and an object in motion stays in motion unless it is acted upon by an unbalanced force. Objects, in essence, resist changes to their state of motion. This force of resistance is called inertia.

**Try This**: To demonstrate inertia for students, place a tennis ball (or other light, harmless object) into a plastic bucket. Ask students what will happen when you turn the bucket upside down. The ball will fall out because the force of gravity acts upon it. Now say you will show them a force that can actually defy gravity, called inertia. Have students each take turns holding the bucket and swinging it around in a vertical circle so that the object stays in on each swing. Explain that this force is the same force they feel pushing them to one side when riding in a car or on a bike that takes a sharp curve.

### Seesaw Lever Lift

**Materials Needed:**

- Access to at least one seesaw
- Heavy objects for students to practice lifting, such as big dictionaries or plastic bins

**Science Concept**: It is easy to lift a piece of paper or a feather, but could you lift a sack of rocks? When you try to lift something heavy, gravity pulls against it. The more mass that you are trying to lift, the harder the pull. People have learned to outsmart gravity by using simple machines such as levers.

**Try This**: For this two-part activity, you’ll need a heavy object that students can safely lift — such as a big dictionary — and a seesaw, which will act as a lever.

**Questions**: First, ask pairs of students to predict which will require more force: lifting the object up into the air with their hands or lifting it by using a lever. Have pairs test their predictions. The students should place the object on the lowered end of a seesaw and push down on the other end. They should discover that using a lever to raise an object requires less force than directly lifting the object. Next, challenge students to test, and then answer, why it matters where you sit on the seesaw. What happens if you sit close to the center?

### Body Balancing

**Materials Needed:**

- Access to an empty wall or side of a building

**Science Concept**: An object’s center of gravity, or center of mass, is the point where the object is perfectly balanced on all sides and the weight of the object appears concentrated. Each person has a center of gravity.

**Try This**: Ask students to form pairs and observe one another from the side as each tries to lean forward, keeping their legs straight, and touch the ground in front of his or her toes. Ask them to observe how the body changes to stay in balance — when one part moves forward, another part leans back.

**Questions**: Ask the students to predict answers for the following questions, then test their answers: What would happen if you tried to touch your toes with your heels pressed against the wall? Have students try it against the wall of the school. Is it impossible? Explain that one’s body can’t move its center of mass too far to one side without losing balance. What if two students leaned against each other? Can students identify where the pair’s center of gravity is?

### The Best Ride Ever

**Materials Needed:**

- Plain, white paper, one piece per student
- Pencils, pens, or markers

Use the following questions to get the students thinking:

- Can you think of a way to make our playground more fun?
- What kind of rides and equipment would you like to see?
- How can you use physics to create the best ride ever?

Now ask your students to design the best ride ever! Challenge the students to choose one piece of playground equipment and brainstorm ways to improve it or invent an entirely new piece of equipment. Invite students to sketch their designs on paper, adding descriptions of what each invention does and explaining why it is the best ride ever. Remind students to use as many physics words in their descriptions as possible!

- Subjects:Science, Science Experiments and Projects, Force and Motion, Gravity, Simple Machines, Recess

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