ScienceFreePrintable

Forces in Action!

A free science worksheet ready for your classroom. Open in Kuraplan to grab the print-ready PDF, customize it for your students, or generate a fresh version in seconds.

Download now

Name:Date:

Forces in Action!

Use the scenario and force information below to investigate how forces change motion. Show calculations where needed and include units.

Charlotte’s run

Charlotte starts from rest at the top of a ramp. She pushes off and rolls down, then crosses the flat concrete. Friction between her wheels and the ground, and air resistance, oppose her motion. At the end, she presses her foot against the ground to slow down. For the questions below, treat forces in opposite directions as subtracting from one another.

1.While Charlotte is rolling across the flat ground, name the downward force and the upward contact force acting on her and her skateboard. Explain why these two forces do not make her move vertically.

2.Charlotte rolls at a steady speed in a straight line. Are the forces on her skateboard balanced or unbalanced? State what this tells you about the resultant force.

Balanced; the resultant force is zero.
Unbalanced; the resultant force is zero.
Balanced; a forward resultant force keeps its speed steady.
Unbalanced; the resultant force must point upwards.

3.At a different moment, on the flat, Charlotte and her skateboard have a total mass of 50 kg. Her push provides a 120 N forward force. Friction and air resistance together provide 35 N backwards. Calculate the resultant force and state its direction.

4.Use the resultant force from Question 3 and Newton’s second law, F = ma. Calculate Charlotte’s acceleration. Include the correct unit.

5.Charlotte stops pushing, but her skateboard keeps rolling for a while. Explain why it does not stop instantly, and identify the forces that eventually slow it down.

Nathan tests a board

Nathan measures the horizontal forces on a skateboard as it rolls over flat concrete. The forces are shown in the table.

Trial

Forward force

Backward force

40 N

65 N

25 N

15 N

30 N

6.For trials A, B and C, calculate the horizontal resultant force, including its direction. In which trial would the skateboard’s speed stay constant if the forces remained unchanged?

7.Rawiri is travelling quickly when he presses his foot on the ground to stop. Explain how the stopping force changes his motion, and why stopping from a higher speed generally needs more time or distance.

8.Nathan wants to find out whether a rougher surface increases the friction on a rolling skateboard. Describe one variable he should change, one he should keep the same, and one measurement he could make.

9.A helmet does not prevent a rider from moving during a fall, but it can reduce the risk of head injury. Explain how increasing the time taken for the head to stop can reduce the force of an impact.