The Heavy Cart and the Fast Cart
Sam's cart carries two heavy bricks and rolls slowly. Maya's empty cart rolls fast.
Both carts will hit the same block. Which one will push it further?
Page 1
Science · Grade 4 Science
Chapter 1: Energy and Motion
How hard it hits, and why.
Sam's cart carries two heavy bricks and rolls slowly. Maya's empty cart rolls fast.
Both carts will hit the same block. Which one will push it further?
Make your guess to turn the page.
Still to come: 9 pages · Words to Know · What We Learned · 4 questions · Explain It in Writing · Ask and Wonder
The idea this lesson is working on — Children expect the heavier thing to hit harder. Sam's cart is three times heavier than Maya's and still loses, 12 units to 16, because speed is counted twice. Ask your child to work the number out before looking at the result: a rule that gets a surprising case right before the run is a rule worth trusting.
Why crumple zones exist — Padding does not reduce the energy in a crash; energy cannot be destroyed. A crumple zone, a helmet or a crash mat squashes, which spreads the stop over a longer time and distance, so the force on the people inside is much smaller. The energy still has to go somewhere; the design decides where and how quickly.