Mass & Acceleration
2nd Law of Motion
Do Now
Ranking Task
Rank the Net Force on each object
from greatest to least.
June 2015
Simulating Zero g
What's a Vomit Comet? — NASA
NASA and B.Y.U.
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The Formula
Mass & Acceleration Are Inversely Proportional
The acceleration a given force will produce on an object is inversely proportional to the mass of the object
[ Flash ]
Object A
F = 10 nt
m = 2 kg
a = 5 m/s2
Object B
F = 10 nt
m = 4 kg
a = ?
Object A
a = 5 m/s2
Object B
a = 2.5 m/s2
| a | m |
|---|---|
| ×2 | ×1/2 |
| ×1/2 | ×2 |
| ×1/3 | ×3 |
| ×3 | ×1/3 |
| ×1/4 | ×4 |
| ×3/2 | ×2/3 |
“Why do all bodies accelerate at a rate of 10 m/s2 (9.8 m/s2)”
(neglecting friction)
Inertial Mass
Solve for m — finding mass using motion and force
What is the mass of the body
that produced the plot above?
Enrichment
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. The same net force acts on two carts. Cart B has twice the mass of cart A. Compared with cart A, cart B's acceleration is…
2. A 10 N net force acts on a 4.0 kg object. What is its acceleration?
3. A net force of 6 N gives an object an acceleration of 2 m/s². What is its mass?
4. For a constant net force, how are mass and acceleration related?
5. Without air resistance, a heavy rock and a light rock fall with the same acceleration. Why?
Weighing an Astronaut in Space
Bathroom scales do not work on the International Space Station. Instead, astronauts measure their mass with a device that pushes them with a known force and measures their acceleration. In one trial, the device applied a net force of 120. N and measured an acceleration of 1.6 m/s².
What is the astronaut’s mass?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. For a second astronaut, the device again applies a net force of 120. N and measures an acceleration of 1.5 m/s². Substitute numerical values into a mathematical representation that can be used to determine this astronaut’s mass. Then calculate the mass.
C2. Which graph best represents acceleration versus mass when the same net force is applied?
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C4. The device is reprogrammed to accelerate the 75-kg astronaut at 2.0 m/s². Determine the net force the device must apply.
C5. Which statement about the astronaut’s mass and weight on the space station is correct?
C6. The astronaut sits on a seat that moves with her, and the seat has its own mass. Describe how this affects the mass the device calculates, and explain how engineers can correct for it.
