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6
votes
1answer
129 views

Why are angular velocity and angular frequency not measured in Hertz?

Recently, I was doing my homework and I found out that Angular Velocity and Angular Frequency can be calculated using $\omega=v/r$. This means the units of angular velocity and angular frequency are (...
0
votes
1answer
68 views

Constants of proportionality in Force Equations/ Physics in General

I was in physics class and we were talking about the gravitational constant G (6.67 x 10^-11 Nm^2/Kg^2). The question came up: "Why does $F= (GMm)/r^2$ have a constant of proportionality and not $...
0
votes
1answer
35 views

Units caculation in the article don't match for reynolds numbers higher than 1

The article discusses the forces acting on a falling object in respect to the drag forces and reynolds numbers. The article suggests for varying Reynolds numbers, the force of drag equation is written ...
2
votes
2answers
138 views

Infinite plane gravity: what is “mass density per unit area”?

Recently I learned that the gravity of an infinity plane is independent of the distance from that plane. In fact it is $$g = 2\pi G \sigma$$ where $\sigma$ is "the mass density of the plane per unit ...
-1
votes
1answer
89 views

Angular Momentum calculation not adding up — Where is my error? [closed]

I'm recreating a calculation from this paper. The authors calculated the angular momentum (L) of a spinning disc with mass = 114.7 grams (0.1147 kg) and radius = 4.75 cm (0.0475 m). The disc spins at ...
2
votes
2answers
235 views

Multiplication of units

I can understand the operation of dividing two units for example: 1 m/s it means that the object covers the distance of 1m in one second but really I can not understand the operation of multiplication ...
0
votes
1answer
109 views

The Gauss's law for gravitational field and the unit system

Here $g$ is the gravitational field, $G$ is the gravitational constant, and $M$ is the total mass in the volume $V$. I wonder if this formula holds for any unit system. That is, does the coefficient $...
-1
votes
1answer
195 views

Why is $k$ taken as 1 in the derivation of $F=kma$? [duplicate]

In the derivation of F=ma, when we reach the point F=kma, we take k=1. Why can't we take 'k' as some other value?
1
vote
3answers
135 views

Why the time period cannot depend upon the angular velocity and angular acceleration of the pendulum?

To derive the time period $T$ of a pendulum using dimensional analysis it is assumed that it depends upon the mass $m$ of the bob, the length of the string $\ell$, the acceleration due to gravity $g$ ...
14
votes
7answers
3k views

Why are work and energy considered different in physics when the units are the same?

There is a question that explains work and energy on stack exchange but I did not see this aspect of my problem. Please just point me to my error and to the correct answer that I missed. What I am ...
0
votes
2answers
108 views

In a force model, $F = ma$, how to understand the units?

For instance, in an aerodynamic force model, the force terms can be lift terms, drag terms, both of which have translational velocities as factors in their models; but, velocities are in units of, say,...
0
votes
1answer
116 views

How is it possible that SI units allow us to write $F=ma$ without an extra constant?

This question follows off the other question posted here: How do we know that $F = ma$, not $F = k \cdot ma$ I hear that when writing $F = kma$ we can always set $k$ to be $1$. How is that possible? ...
0
votes
3answers
189 views

How can I justify $g/l = 1$ in the simple pendulum equation?

The differential equation for a simple pendulum can be given as, $$\frac{\mathrm{d}^2\theta}{\mathrm{d}t^2} + \frac{g}{l}\sin\theta = 0$$ In some notes I found that $g/l$ can be assumed as $1$ (i.e $...
-1
votes
1answer
94 views

Is this differential equation (for damped & driven physical pendulum) physically valid?

Following is the equation of motion for a physical pendulum which is damped and driven by a force of frequency $f$: $$\frac{d^2 \theta}{dt^2} + b \frac{d\theta}{dt} + sin(\theta) = Tsin(2\pi ft)$$ ...
-2
votes
1answer
50 views

In this energy conservation problem, why are the answers different with different units? [closed]

Really basic question, but basically I'm given a change in height in centimeters (that's how I measured it). From that, I'm supposed to find the initial kinetic energy. $KE_i = PE_f$ After doing ...
3
votes
1answer
290 views

Newton's Second Law of Motion

Newton originally wrote his second law as: "The rate of change of momentum of a body is directly proportional to the resultant force applied to the body, and is in the same direction as the force." ...
1
vote
2answers
158 views

Visualizing Physical Units in Phyiscs

I do best in physics when I can make sense of the units that accompany values, and I do this by visualizing in my mind what is happening. Take for instance, $v=\frac{s}{t}$. When I think of velocity I ...
0
votes
1answer
63 views

Definition of unit of force [closed]

As we know $1\ \mathrm{N}$ is the force which can accelerate $1\ \mathrm{kg}$ mass with $1\ \mathrm{m/s^2}$ acceleration. But for which surface is this definition given? I mean a $1\ \mathrm{kg}$ ...
1
vote
1answer
3k views

Difference between kilogram-force and kilogram

I know that a 1 kilogram-force is the force of 1 kilogram acted upon by 1 standard unit of gravity (9.80665 m/s^2). However, in torque descriptions I find that some use $kgf*cm$ while others use $...
1
vote
3answers
6k views

How is it that Force = Mass $\times$ Length / Time ^2?

I understand how $F=ma$ but what I am looking for is a diagram, idiom or concept that explains how force can be explained (in a partial layman's terms) as a combination of the dimensions; Length, Mass ...
1
vote
4answers
2k views

Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?

In classical physics we often cast an analogy between translational and rotational systems Force < > Torque Energy < > Rotational Energy Momentum < > Angular Momentum and considering SI ...
3
votes
1answer
353 views

Units of acceleration & Newton's 2nd Law

I tried to use Newton's second law, $F=ma$, to calculate the acceleration of an object. \begin{align}\frac{F}{m}&=\frac{ma}{m} \\ a&=\frac{F}{m}=\frac{30\,\rm N}{1.2\,\rm kg}=25\rm\frac{N}{kg}...
1
vote
2answers
762 views

Convert constant of gravitation to days and AUs [duplicate]

I'm working on a problem with celestial bodies and for my purpose days and AUs are more appropriate units than seconds and meters. So I tried to convert the constant of gravitation, $G$, like this: $$...
2
votes
1answer
248 views

Does a 27 hp engine output the same amount of energy as lifting a 1 ton stone block almost 3 meters per second?

I’m trying to get a sense of how much energy a 27 horsepower engine outputs. 27 hp $=$ 20 133 watts (joules/second). Potential energy can be calculated as $E = mgh$ where $g = ~9.8\ m/s^2$ on earth. ...
2
votes
2answers
694 views

Understanding units manipulation (speed of falling coconut after 20m)

When I was on holidays, I was told a story about how someone passing under a palmtree and almost got a coconut fall on his head. Given that these palmtrees where about $20m$ high, we wondered at what ...
46
votes
10answers
43k views

Why is torque not measured in Joules?

Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$. This means the units of torque are Newton meters. Work & Energy are also measured in Newton ...
0
votes
2answers
4k views

static friction problem without mass

I am having trouble with a physics problem. The problem is as follows: A car is traveling at 54.0 mi/h on a horizontal highway. A) If the coefficient of static friction between road and tires on a ...