Swinging Forces

SCIENCE CONCEPT: What makes a swing, swing? As we pump our legs, we build momentum, which pushes the swing 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. 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 chalk diagram of each of the three points and identify at each point the force that controls the movement: Is it momentum or gravity? (When the swing moves from the lowest point up to either peak, the force is momentum; when the swing falls down from either peak to its lowest point, the force is gravity.)

Slip Sliding Away: Friction Comparison

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. Ask students to predict which materials, including their own clothing, would 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

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 could get in their way? Invisible air! Next, hold up two identical pieces of paper, and crumple one into a ball. Ask students to predict which one will fall faster. Then have student pairs investigate by each student dropping a piece 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? Air resistance! More air pushes back against the flat piece, slowing its fall.

 

Stronger Than Gravity

SCIENCE CONCEPT: Is there any force that can defy gravity? Actually, yes! Centrifugal force pushes objects that are moving in a circular path towards the outside of that path, keeping them moving in a circle.

TRY THIS: To demonstrate centrifugal force 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, of course. Why? Gravity! Now say you will show them a force that can actually defy gravity, called centrifugal force. 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

SCIENCE CONCEPT: It´s really 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´re lifting, the harder the pull. But long ago, people 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. 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 (placing it on the lowered end of a seesaw and pushing on the other end). Have pairs test their predictions. They should discover that using a lever to raise an object requires less force than directly lifting does. 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

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 where the weight of the object appears concentrated. Each person has a center of gravity, too!
TRY THIS: Ask students to form pairs and observe one another from the side as each tries to lean forward, with straight legs, 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. Then ask for predictions: 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

Ask your students: Can you think of a way to make our playground more fun? What kind of rides and equipment would you like to see? Then challenge them 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 glossary words in their descriptions as possible!