Science · Kindergarten · Force, Motion, and Interactions · Weeks 1-9

Changing Direction with Collisions

Students investigate how objects collide and how surfaces affect the path of a moving toy or ball.

• Common Core State Standards
• K-PS2-1
• K-PS2-2

About This Topic

This topic shifts students from simply starting motion to understanding that forces can also change direction. When one object collides with another or with a surface, something predictable happens: the moving object slows, stops, or changes path. Aligned with K-PS2-1 and K-PS2-2, this topic introduces the idea that interactions between objects produce observable, repeatable patterns students can describe and predict.

Surface texture plays an important role here as well. A ball rolling across carpet behaves differently than one on tile, so students learn early that the path of a moving object depends on both the collision and the surface it moves on. In US elementary classrooms, this concept is commonly explored through simple rolling games and building activities that make the physics immediate and visible.

Active learning is the natural fit for collision science. Students who physically roll a ball down a ramp and watch it hit a block, then rearrange the block to redirect the ball, discover directionality through their own iteration. This cycle of predict, test, and revise is the core scientific practice, and it is most meaningful when students can touch and change the variables themselves.

Key Questions

1. Analyze how we can change the direction of a moving ball without stopping it.
2. Predict what happens when a moving object hits a stationary wall.
3. Explain how the shape of an object changes how it rolls or slides.

Learning Objectives

• Predict the change in direction of a toy car when it collides with a stationary object.
• Compare the path of a rolling ball on two different surfaces, such as carpet and tile.
• Explain how the angle of a ramp affects the speed and distance a toy travels after a collision.
• Demonstrate how a gentle push versus a hard push changes the outcome of a collision with a wall.

Before You Start

Starting Motion

Why: Students need to understand how to make objects move before they can explore how to change their direction.

Push and Pull

Why: Understanding that pushes and pulls are forces that cause motion is foundational to understanding how collisions involve forces.

Key Vocabulary

collision	When two objects hit each other, like a ball hitting a wall or another ball.
force	A push or a pull that can make something move, stop, or change direction.
surface	The outside part of something, like the floor, a wall, or a ramp, that a moving object touches.
direction	The way something is moving or pointing, like forward, backward, left, or right.

Watch Out for These Misconceptions

Common Misconception

A ball always stops completely when it hits something.

What to Teach Instead

Many students expect a full stop at every collision. Using a bouncy ball against a wall, which bounces back rather than stopping, directly challenges this assumption. Active testing with multiple collision types builds a more nuanced mental model.

Common Misconception

Shape does not affect how an object moves.

What to Teach Instead

Students may think a sphere and a cube roll or slide equally well. A side-by-side test of a wooden cube versus a rubber ball on the same ramp shows clearly that shape matters, setting up later learning about geometry and design.

Active Learning Ideas

Inquiry Circle: Redirect the Ball

Pairs set up a simple ramp with a wooden block at the bottom as a wall. They roll a ball, mark where it ends up with a sticker, then tilt the block to a different angle and test again, comparing three different setups to see how the direction of the ball changes.

30 min·Pairs

Simulation Game: Human Collision

Students stand in a line about three feet apart. The first student rolls a playground ball to the second, who redirects it gently without stopping it to a third. The class observes and discusses whether the ball stopped or changed direction based on how it was touched.

15 min·Whole Class

Think-Pair-Share: The Stopped Ball

Hold up a ball and a foam block and ask what will happen to the ball after it hits the block. Students share predictions in pairs, then watch the demo and discuss whether the ball stopped or changed direction based on the block's weight and position.

15 min·Pairs

Real-World Connections

• Bumper cars at amusement parks use collisions to create fun, changing directions rapidly when they bump into each other or the arena walls.
• Bowling alleys use the principles of collision and surface friction. The ball collides with pins, and the oiled lane surface affects how the ball rolls and curves toward the pins.
• Children playing soccer or kickball experience collisions constantly as the ball hits players' feet, the ground, or goalposts, changing its direction and speed.

Assessment Ideas

Exit Ticket

Give students a toy car and a small ramp. Ask them to roll the car down the ramp and observe its collision with a block. On their exit ticket, they should draw a picture showing the car's path before and after the collision and write one sentence about how the direction changed.

Discussion Prompt

Gather students in a circle with various balls and surfaces (e.g., a smooth mat, a carpet square, a piece of sandpaper). Ask: 'What happens when we roll this ball on the carpet? Now, what happens when we roll it on the smooth mat? Why do you think the ball moves differently?'

Quick Check

Set up a simple obstacle course with a wall or a row of blocks. Have students take turns pushing a toy car or ball through the course. Observe if they can predict and explain why the car changes direction when it hits an obstacle.

Frequently Asked Questions

How do I connect collision observations to K-PS2-2 in Kindergarten?

K-PS2-2 asks students to analyze data to determine if a design solution changes the speed or direction of an object. For a Kindergarten collision experiment, students compare whether adding a foam bumper versus nothing changes where the ball ends up. That comparison between two conditions is the analysis the standard requires.

What safe materials work best for collision experiments?

Foam blocks, rolled-up socks, soft rubber balls, and empty plastic water bottles make ideal collision objects. They show clear motion effects without safety risk. Avoid hard marbles on bare tile if students are seated on the floor. A cardboard gutter or foam track keeps experiments contained and results visible.

How do I help students record what they observe during collision experiments?

Use before-and-after drawings. Students draw the starting setup, then draw where the ball ended up with an arrow showing the new direction. This simple format works well for non-writers while requiring students to process and represent their observations rather than just saying what happened.

How does collaborative investigation help students understand collisions?

Partners naturally narrate to each other what they see, and this verbal processing is powerful for learning. When one student sets up the collision and the other observes, then they switch roles, both students encode the pattern from multiple perspectives. That dual-role experience deepens comprehension more than individual observation alone.