8th grade Waves that add and cancel worksheet

Waves that add and cancel

Grade 8 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Heights above the rest line are positive. Two ripples cross in Bo's pond tank, and their heights add. What is the height of the combined wave at point U?
2. 2.

   Heights above the rest line are positive. Two waves overlap on a pond, and their heights add. What is the height of the combined wave at point T, Esme?

3. Read this first

   Two waves on a rope (example data)

   point	wave A (cm)	wave B (cm)	A + B (cm)
   R	3	−3	0
   S	2	2	4
   T	4	−1	3
   U	0	0	0

4. 3.

   At which point do the two waves cancel completely, Jun?

   • T, where a trough meets a crest, so the two cancel there
   • U, where the sum is 0 cm because both waves are at rest
   • R, where equal and opposite heights add to 0 cm
   • S, where the two waves are equal and give the largest sum
5. 4.

   At which point is the combined wave tallest above the rest line, Kira?

   • S, where two crests of 3 cm and 2 cm add to 5 cm
   • R, where the two crests are equal in height at 1 cm each
   • U, where a 4 cm crest meets a 4 cm trough, the strongest meeting
   • T, where wave A is the biggest single wave at 4 cm in size
6. 5.

   At point S, how does wave B change wave A's height, Luz?

   • B cancels it completely, since a trough meets the crest there
   • B changes nothing, since 1 cm is much smaller than 4 cm
   • B lowers it from 4 cm to 3 cm, since B's height there is negative
   • B raises it from 4 cm to 5 cm, since B's size of 1 cm gets added to A's height

7. Two pulses on a rope (example data)

   time (s)	3 cm pulse at (m)	2 cm pulse at (m)	tallest point on the rope (cm)
   0	1	9	3
   1	5	5	5
   2	9	1	3

8. 6.

   Milo films two pulses on a rope. What do the readings show about the pulses?

   • They merged: the 5 cm bump at 1 s replaced both, so one pulse was left after that
   • They bounced: at 1 s they met and each went back toward the end it started from
   • The 3 cm pulse absorbed the 2 cm pulse, so the readings after 1 s show a single pulse at the far end
   • They passed through: they added to 5 cm at 1 s, then the 3 cm pulse reached 9 m

9. Two crests on a rope (example data)

   time (s)	4 cm crest at (m)	2 cm crest at (m)	rope height at 5 m (cm)
   0	1	9	0
   2	5	5	6
   4	9	1	0

10. 7.

    Why is the rope 6 cm high at 5 m when the pulses meet at 2 s, Pia?

    • The crests pushed against each other at 5 m, and the push raised the rope above both
    • The crests bounced off each other at 5 m and stacked up for a moment before moving back
    • Both crests were at 5 m, so their heights added, 4 + 2 = 6 cm, and then each moved on
    • The 4 cm crest absorbed the 2 cm crest and stayed 6 cm tall as it moved on to 9 m

11. Two ripples at one spot (example data)

    time (s)	ripple A (cm)	ripple B (cm)
    0	2	2
    1	−2	−2
    2	2	2
    3	−2	−2

12. 8.

    Ripples A and B meet at one spot in Ren's pond. What kind of interference does the table show there?

    • Constructive, but the combined ripple is still 2 cm tall, since equal ripples do not add
    • Destructive: the two ripples are the same size at each time, so they must cancel
    • Constructive: the ripples rise and fall together, so the combined ripple is 4 cm tall
    • Destructive: the ripples rise and fall together, so they cancel out at that spot

13. Two ripples at another spot (example data)

    time (s)	ripple A (cm)	ripple B (cm)
    0	2	−2
    1	−2	2
    2	2	−2
    3	−2	2

14. 9.

    Ripples A and B meet at another spot in the pond. What kind of interference does the table show, Tala?

    • Constructive: the ripples are the same size, so they build up a combined ripple that is 4 cm tall
    • Destructive: the sums are 0 cm, so these ripples are destroyed for good everywhere
    • Neither: the sums are 0 cm, so no ripples ever reached this spot from either side
    • Destructive: the ripples rise and fall opposite each other, so the water stays flat there

15. Two ripples at a third spot (example data)

    time (s)	ripple A (cm)	ripple B (cm)
    0	3	1
    1	−3	−1
    2	3	1
    3	−3	−1

16. 10.

    Ripples A and B meet at a third spot in the pond. What does the table show, Zee?

    • Destructive: the 1 cm ripple weakens the 3 cm ripple to a combined ripple of 2 cm
    • Constructive, with a combined ripple 2 cm tall, found by subtracting 1 cm from 3 cm
    • Constructive, with a combined ripple 4 cm tall, since the ripples rise and fall together
    • Constructive, with a combined ripple 3 cm tall, since the larger ripple wins the meeting