Waves that add and cancel
Grade 8 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
Heights above the rest line are positive. Two waves overlap on Ari's rope, and their heights add. What is the height of the combined wave at point S?
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?
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?
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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 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
- S, where the two waves are equal and give the largest sum
- R, where equal and opposite heights add to 0 cm
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
- T, where wave A is the biggest single wave at 4 cm in size
- U, where a 4 cm crest meets a 4 cm trough, the strongest meeting
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 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
- The 3 cm pulse absorbed the 2 cm pulse, so the readings after 1 s show a single pulse at the far end
- They bounced: at 1 s they met and each went back toward the end it started from
- They passed through: they added to 5 cm at 1 s, then the 3 cm pulse reached 9 m
A crest and a trough on a rope (example data)
time (s) 3 cm crest at (m) 3 cm trough at (m) tallest point on the rope (cm) 0 1 9 3 1 5 5 0 2 9 1 3 A crest and a trough meet on a rope and the rope goes flat. What do the readings show, Noah?
- They destroyed each other at 1 s, so the 3 cm readings at 2 s must come from a new pair of pulses
- They bounced at 1 s, so the crest and the trough went back to the ends where they began
- They cancelled at 1 s but were not destroyed: the crest and trough are back by 2 s
- They merged into a flat rope at 1 s, and the flat rope then split into a new crest and trough
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 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 4 cm crest absorbed the 2 cm crest and stayed 6 cm tall as it moved on to 9 m
- 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
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 Ripples A and B meet at another spot in the pond. What kind of interference does the table show, Tala?
- Neither: the sums are 0 cm, so no ripples ever reached this spot from either side
- Destructive: the sums are 0 cm, so these ripples are destroyed for good everywhere
- Constructive: the ripples are the same size, so they build up a combined ripple that is 4 cm tall
- Destructive: the ripples rise and fall opposite each other, so the water stays flat there
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 Ripples A and B meet at a third spot in the pond. What does the table show, Zee?
- Constructive, with a combined ripple 4 cm tall, since the ripples rise and fall together
- Destructive: the 1 cm ripple weakens the 3 cm ripple to a combined ripple of 2 cm
- Constructive, with a combined ripple 3 cm tall, since the larger ripple wins the meeting
- Constructive, with a combined ripple 2 cm tall, found by subtracting 1 cm from 3 cm