74
votes
Is "Mass" really measuring unit for inertia?
Imagine a 10kg curling stone on a flat ice surface on Earth. If we apply 10N of horizontal force, the stone will accelerate at about 1 meter per second per second. On the Earth, a 10kg stone weighs ...
- 2,104
72
votes
Why does a bowling ball roll down faster on a slope than a tennis ball, yet both hits the ground at the same time if they're dropped from the rooftop?
The easy explanation is that the tennis ball is hollow.
When you merely drop the objects, they are subjected to the same acceleration - the aceleration due to gravity - and nothing else. Conservation ...
- 24.6k
68
votes
Why does mass limit acceleration?
I do not think it is mass that "CAUSES" inertia. Rather mass is DEFINED to be the property of an object which gives it inertia
For example, imagine that you were a theoretical observer who ...
- 4,496
66
votes
Accepted
Why did we expect gravitational mass and inertial mass to be different?
"isn't there just one property called m and it just appears in
different equations (e.g. Newton's second law and the law of
gravitation)? In a similar way that (say) frequency appears in many
...
- 4,496
47
votes
What causes a rotating object to rotate forever without external force—inertia, or something else?
Is it inertia that a rotating object will rotate forever without external force? Someone told me that this is not inertia [...]
Well, sort of - it’s somewhat correct to say it is inertia, and ...
- 848
45
votes
Accepted
How would I move if I grew by a factor of 3 in each physical dimension?
Assuming for a moment that your bones are proportionately stronger... (because you are asking about motion, not strength: but see for example this question about scaling in nature) That still leaves ...
- 119k
45
votes
Accepted
Couldn't we always redefine units so that inertial mass and gravitational mass are equal?
To make it clear that it is not obvious it is better to stop using the word "mass" in both cases. So it is better to say that it is not obvious that the inertial resistance, meaning the property that ...
- 1,624
44
votes
Accepted
Why can we calculate moment of inertia, but not inertia?
Classically, the inertia of something is just its mass. If you want an analogous equation, just integrate the mass density $\rho$ of the object over the volume of the object:
$$m=\iiint \text dm=\...
- 58.6k
36
votes
Why did we expect gravitational mass and inertial mass to be different?
Objects have a property called "electric charge". This electric charge decides how strong a force they feel when close to other electrically charged objects. The electric charge of an object ...
- 3,028
35
votes
How many types of inertia are there?
My suggestion is you throw this book away, and use only "good books".
Whoever wrote this book has a very confused mind.
I can vaguely guess what the author might have had in mind when he ...
- 4,448
33
votes
Flying a drone in a moving car/airplane
Very good question! The point is that when the elevator begins to move (either upwards or downwards), it's accelerating, while the drone -- having no force acting on it directly -- is still moving at ...
- 11.5k
31
votes
When a car accelerates relative to earth, why can't we say earth accelerates relative to car?
Isn't it equally plausible to say that the Earth has accelerated from
the point of view of the reference frame of the car?
Yes it is.
The car accelerates because the static friction force exerted ...
- 77.9k
29
votes
Couldn't we always redefine units so that inertial mass and gravitational mass are equal?
Scenario I: I have a white ball and a black ball. In the system of units I've adopted, I discover that:
Gravitational mass of white ball = 2
Inertial mass of white ball = 3
Gravitational mass ...
- 17k
27
votes
When a car accelerates relative to earth, why can't we say earth accelerates relative to car?
The second Newton's law is valid for inertial frames of reference.
If we are for example in a airplane that is braking after landing, any loose object will accelerate forwards, without any force that ...
- 17.1k
26
votes
Accepted
Would you run faster on Mars?
The speed of walking and running depend on pendulum-like motion of the legs. If you walk at different speeds the power used varies, and has a minimum roughly corresponding to the free pendulum motion ...
- 33.4k
22
votes
Why can we calculate moment of inertia, but not inertia?
BioPhysicist is right.
Your confusion comes from the fact that the word "inertia" is not a "technical" term. It refers to a notion that can apply to many things, physical or ...
- 4,448
21
votes
Accepted
How is Newton's first law of motion different from Galileo's law of inertia? If the two are the same, then why is the first law named after Newton?
This is not uncommon in the world of physics. Different scientists might discover certain parts of a theory and some other scientist might come later and be able to incorporate all the previous known ...
- 4,496
21
votes
Accepted
Very strange published papers on Mach's Principle
Having looked at the web site what stands out is the misuse of the concept of Mach's principle; the failure to give quantitative information; the failure to engage the obvious questions; the apparent ...
- 61.8k
21
votes
When a car accelerates relative to earth, why can't we say earth accelerates relative to car?
What breaks the symmetry here?
The accelerations are not symmetric because (proper) acceleration itself is not relative (frame variant). A simple accelerometer can measure the asymmetry. The car’s ...
- 109k
20
votes
How would I move if I grew by a factor of 3 in each physical dimension?
Yes, you would have 27x the muscle mass. However, muscle mass is not actually the factor which defines the strength of a muscle. The strength of a muscle increases based on its cross sectional area, ...
- 51.7k
20
votes
Accepted
Does the bias in a loaded die depend on gravity?
The experimental research paper "Cuboidal Dice and Gibbs Distributions" by Wolfgang Riemer, Dietrich Stoyan, and Danail Obreschkow, (link here) indicates that when symmetry is broken (in ...
- 324
19
votes
What causes a rotating object to rotate forever without external force—inertia, or something else?
At its most basic, an object will rotate forever for the simple reason that there is no preferred direction in space.
Emmy Noether's theorem of 1918 explains how various conservation laws arise from ...
- 11.2k
19
votes
What is the origin of the inertia?
Currently, there is no scientific consensus on why inertia exists, or why the geodesic through spacetime is the least path of energy (ultimately leading to: why do we need to expend energy to move an ...
- 472
15
votes
Why does a bowling ball roll down faster on a slope than a tennis ball, yet both hits the ground at the same time if they're dropped from the rooftop?
I haven't tried this experiment but the first two factors that spring to mind are:
Rolling Friction The bowling ball is hard and smooth while the tennis ball is fuzzy and softer. This would lead to ...
- 8,920
15
votes
Accepted
Do electrons have inertia?
Inertia is the resistance of any physical object to a change in its velocity. This includes changes to the object's speed, or direction of motion. An aspect of this property is the tendency of objects ...
- 235k
15
votes
Accepted
How does classical, Newtonian inertia emerge from quantum mechanics?
I'd go with the Ehrenfest theorem, for the time derivative of the expectation value of an operator $A$:
$$\frac d{dt}\langle A \rangle = \frac 1 {i\hbar}\langle
[A, H]\rangle +\big\langle \frac{\...
- 39.6k
15
votes
How does inertia affect an object suspended in a fluid?
If a submerged object is in hydrostatic equilibrium, that is the buoyancy force and the gravitational force on it exactly balance, it will stop moving because of friction with the fluid it is in. This ...
- 2,007
14
votes
Accepted
How can a flywheel make engine run smoothly?
By adding flywheel makes engine to take more power to spin the flywheel because of its huge mass. Efficiency of the engine drops very low. I can only see more burden than smoothness.
The burden is ...
- 77.9k
14
votes
Is "Mass" really measuring unit for inertia?
Physicists distinguish gravitational mass from inertial mass. In practice we find that gravitational mass is equal to inertial mass, but the distinction is important because conceptually they need not ...
- 11.8k
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