ScienceGrade 3

How Do Animals Move? Swim, Fly, Run and Wriggle

Muscles contract — they get shorter and pull — then relax; working together they move body parts

Learning Objective

Students will learn that animals move in different ways — swimming, wriggling, flying, running, and waving tentacles — and that almost all of these movements share one secret: muscles that contract (pull shorter) and relax to move body parts.

What You'll Learn

A fish has strong muscles down its sides: one side contracts while the other relaxes, bending the body side to side so the tail pushes against the water — fins help it balance
An earthworm uses muscles to push its front forward, then pull the rest of its body along — strong enough to burrow through soil
Birds and insects use strong muscles to move their wings — a bird's wings are modified front limbs, an insect's wings attach to its body
Legged animals (insects, lizards, birds, mammals) bend their legs at joints when muscles contract — the cheetah is the fastest runner on land
A sea anemone looks like a plant but is an animal — it waves muscular tentacles to catch tiny prey

Words to Know

Muscle: A body part that can get shorter and pull to make you move; The muscles in my legs help me jump and run.
Contract: When a muscle squeezes shorter and pulls; When the fish's side muscles contract, its body bends.
Propel: To push something forward; The fish's tail propels it through the water.
Fin: The flat body parts a fish uses to balance and steer; The fish's fins keep it steady while its tail does the pushing.
Tentacle: A long bendy arm-like body part used to grab or feel; The sea anemone waves its tentacles to catch tiny food.
Burrow: To dig or push through soil or sand; The earthworm burrows through the garden soil.
Joint: The bendy spot where two body parts meet; Your knees are joints that let your legs bend when you run.

Check What You Learned

Quick Quiz

1 / 5

What do muscles do to move a body part?

Fun Facts

Muscles move animal bodies by contracting — becoming shorter and pulling — then relaxing; pairs and groups of muscles work together
Source: NGSS / Britannica Kids
A fish has strong muscles along the sides of its body; muscles on one side contract while the other side relaxes, bending the body side to side so the tail pushes against the water
Source: Britannica Kids / elementary life science texts
A fish's tail helps propel it forward while its fins help it balance and steer
Source: Britannica Kids
Earthworms use circular and lengthwise muscles: some contract to push the front of the body forward, others pull the rest of the body along — strong enough to burrow through soil
Source: Britannica / elementary life science texts
Birds use strong chest muscles to move their wings up and down; a bird's wings are modified front limbs
Source: Britannica Kids
Insects also use muscles to flap their wings, but insect wings attach directly to the body — they are not modified limbs
Source: Britannica / elementary life science texts

Lesson Info

Grade 3

2026-11-07

Standards Alignment

3-LS1-1
Structure and function — animals have internal and external structures (like muscles and limbs) that function to support survival, growth, and movement
TEKS 3.13A
Explore how structures and functions of animals — such as fins, wings, legs, and tentacles — allow them to survive in their environment
CCSS.ELA-LITERACY.RI.3.3
Describe the relationship between scientific ideas in a text — how muscle contraction causes each animal's different way of moving

Play the whole series

Episode 9 of animal superpowers