Forces and Motion — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Two Grade 3 students push a box in opposite directions with equal force. What happens?
A) The box does not move because forces are balanced
B) The box speeds up in one direction
C) The box lifts off the floor
D) The box bounces back and forth
In Grade 3, balanced forces add to zero, so the box stays still even though both students are pushing.
2. A cart is rolling forward. A Grade 3 student now pushes it forward with more force. What happens?
A) The cart stops right away
B) The cart speeds up in the forward direction
C) The cart turns around
D) The cart keeps the same speed
In Grade 3 science, an unbalanced push forward increases the total force, so the cart speeds up.
3. Two teams are tied in tug-of-war. One team then pulls harder. What will happen?
A) The rope stays still
B) The rope breaks in two
C) The rope moves toward the stronger team
D) Both teams fall down at once
In Grade 3, when one team pulls harder, forces become unbalanced, and the rope moves toward that team.
4. A book rests on a Grade 3 desk without moving. Which statement is true?
A) No forces are acting on the book
B) Only gravity acts on the book
C) Gravity and the desk push are balanced
D) The book is about to fly up
In Grade 3, gravity pulls the book down while the desk pushes up; these balanced forces keep it still.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When forces on an object are balanced, its motion does not change.
In Grade 3 science, balanced forces keep an object's motion the same, whether it is still or moving.
2. When forces are not equal, we call them unbalanced forces.
In Grade 3, unbalanced forces add to a nonzero total and cause the object's motion to change.
3. A still object has forces that are balanced or no forces acting at all.
In Grade 3 science, an object stays still when forces balance to zero, like a book on a desk.
4. To speed up a moving cart, you need an extra push in the same direction.
In Grade 3, an extra forward force makes the total force unbalanced, so the cart speeds up.
5. If balanced forces become unbalanced, the object will change its motion.
In Grade 3 science, unbalanced forces change motion by speeding up, slowing down, or changing direction.