6
votes
2answers
358 views

A force opposing Gravity

Every Action Has An Equal and Opposite Reaction (Newton's Third Law.) If this is the case, does gravity have an equal-opposing force? From asking around I still haven't got a very clear answer; ...
-3
votes
0answers
15 views

calculate gravitational force [on hold]

an object weighs 977N on the surface of the earth and 244.25N if the earth is remoulted. The radius of earth is 6.4×10$^4$m and its mass is 6×10$^{24}$kg. Calculate the radius of remoulted earth and ...
3
votes
2answers
73 views

What is the “associated scalar equation” of equations of motion?

In an essay I am reading on celestial mechanics the equations of motion for a 2 body problem is given as: $$\mathbf{r}''=\nabla(\frac{\mu}{r})=-\frac{\mu \mathbf{r}}{r^3}$$ Fine. Then it says the ...
0
votes
1answer
33 views

What does an $n$-body system with constant $T$ and $U$ look like?

Can someone give an example of a system where the kinetic $T$ and potential $U$ energy are constant (but not zero)? Here's what I have in mind: Say you have $n-1$ satellites of negligible mass ...
3
votes
3answers
54 views

What is the intuition behind $gt^2/2$ equalling the distance something falls after $t$ seconds?

Let's say $g=10\ \text{m/s}^2$ and it drops for $3$ seconds. For the first second it will drop $10\ \text{m}$, the second it will drop $20\ \text{m}$ ($10 + 10$) and the third second it will drop $30\ ...
1
vote
1answer
47 views

Reduced mass and harmonic mean

In two-body problems, a reduced mass has the form: $\frac{m_1 m_2}{m_1+m_2}$, which by appearance, is half of the harmonic mean of $m_1$ and $m_2$: ...
0
votes
1answer
59 views

Why is the range for a particle thrown at 90 degree same as that of a particle thrown at 0 degree?

There is a derivation given in my book which concludes to the fact that the range is same for two angles of projection, provided they are complementary. I fail to understand this fact. For example, ...
9
votes
2answers
1k views

Put a bullet into orbit around the moon

While I was watching this beautiful video, the absence of air friction pushed me to ask myself: While standing on the surface of the moon, what is the initial velocity by which you can fire a bullet ...
0
votes
1answer
51 views

Gravity and Mass

Two bodies of equal size and mass meet in space. My question is: will they attract each other equally or will their attraction cancel each other out?. Also: how long does it take for the two bodies ...
2
votes
1answer
62 views

How does angular momentum transfer between a planet and its moon?

Could you explain how a moon draws angular momentum from a planet? I know that the gravitational force transfers momentum, but I don't understand the mechanics behind it.
7
votes
3answers
100 views

Leading-order cause of diurnal (not semidiurnal) variations in $g$?

The following graph shows the result of a very impressive differential measurement of the gravitational field in Boulder, Colorado, over a period of a couple of days. Floris got it from a ...
4
votes
1answer
184 views

Variation in measurements of $g$ on the Earth's surface due to the Moon's gravity

A book, Exercises for the Feynman Lectures on Physics, has recently been published. It consists of homework problems to provide practice with the techniques and concepts used in the famous Feynman ...
-1
votes
1answer
57 views

Please explain these equations relating to Newtonian gravity [closed]

Here is an extract from some badly-written slides: A planet in an orbit with radius $R$ having a period $T$ falls through a distance of $R$ in a time $T/4$. A planet has a speed of $R/T$ and an ...
26
votes
5answers
4k views

Which ball touches the ground first?

This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes ...
1
vote
1answer
51 views

Torque due to Gravity

I have learned that a torque on an object due to the gravity can be calculated as if the gravity acts on the center of mass of the object when the object is near the surface of the earth. Now I want ...
1
vote
0answers
58 views

How to find the force to cause certain trajectory? [closed]

So I got a little board today and decided to do some physics. What I came up with is confusing me alot. Say someone throws a rock and when this happens you get the known's of. From here is there a way ...
0
votes
2answers
39 views

How would an earth-spanning ring around the equator behave?

If a ring/belt would be constructed of a sufficiently strong material around the entire equator at 100m height from the surface assuming the land/water beneath is flat (no mountains get in the way), ...
0
votes
1answer
34 views

What will be the acceleration of an object $A$ when its released by another object $B$ moving with an upward acceleration $a$?

What will be the acceleration of an object $A$ when its released by another object $B$ moving with an upward acceleration $a$? Will the acceleration of the object $A$ be more than the acceleration due ...
1
vote
1answer
71 views

Dropping a ball in a fast moving train

If I drop a ball in a train moving at a constant speed, will it land on the spot I aimed it at or a little away as the train has moved while it was in air? If it lands away, will the observer not know ...
13
votes
5answers
1k views

Why are these periods the same: a low earth orbit and oscillations through the center of the earth?

Related: Why does earth have a minimum orbital period? I was learning about GPS satellite orbits and came across that Low Earth Orbits (LEO) have a period of about 88 minutes at an altitude of 160 ...
2
votes
0answers
58 views

How to calculate launch angle for tangentially launched satellites?

What is the value of theta for a satellite not falling back to the Earth if it is launched from the direction tangent to the surface of the Earth? I have found the escape velocity which is 11.18km/s, ...
3
votes
2answers
129 views

What is the mathematical definition of work?

I'm looking for the pure mathematical definition of work, but I haven't yet learned line integrals. My book says that the work due to a force ${\bf F}$ from point $A$ to point $B$ is $$ W= |AB|\cdot ...
1
vote
1answer
42 views

If a planetoid was wet and you spun it would the water move to the equator?

If the moon was alone in space and covered in X feet of water and it began to rotate would it displace to a bias along the equator?
1
vote
0answers
16 views

Is acceleration quadratic or linear outside of a gravity field? [duplicate]

So as I understand it: If you hit a wall at twice the speed you hit four times as hard? I often ask people this and everyone says "at twice the speed you hit twice as hard". $K=\frac{1}{2}mv^2$ is ...
0
votes
3answers
80 views

Why doesn't an orbiting body keep accelerating?

As a physics newbie I'm trying to get a grip on basic orbital mechanics. I think I'm beginning to get grasp on how bodies interact with each other. When a body approaches another body it accelerates ...
2
votes
1answer
76 views

Gravity vs inertia

As stated according to Newton laws of gravity, every object with mass attracts all other object with a force which produces acceleration. Basically there are several forces in the universe which ...
0
votes
1answer
37 views

Kinematics and Energy - Finding the work done in projectile motion

If you are asked to find the work done by gravity on a projectile, the force will obviously be the mass multiplied by gravitational acceleration. What will the displacement be, the horizontal or ...
0
votes
1answer
57 views

Follow up question regarding: Deceleration rate of objects of different mass but the same otherwise

My first question was answered here: Deceleration rate of objects of different mass but the same otherwise . But based on that, here is a follow-up question (I also edited my first post with the ...
2
votes
2answers
57 views

Deceleration rate of objects of different mass but the same otherwise

Using a tennis ball as an example object, if one ball weighs 1 ounce and the other is 2 ounces, and both are struck at 100 mph on the same trajectory, would there be any difference in the deceleration ...
3
votes
2answers
100 views

What does an applied force on an already accelerating object do?

I'm a big beginner having only taken Grade 11 high-school physics. Imagine this situation: an object is accelerating north, and while it's accelerating, it's 'hit' by a northward force. To me it ...
52
votes
4answers
6k views

Moon's pull causes tides on far side of Earth: why?

I have always wondered and once I even got it, but then completely forgot. I understand that gravity causes high and low tides in oceans, but why does it occur on the other side of Earth?
23
votes
6answers
3k views

Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
3
votes
2answers
87 views

Does the opening angle of the cone matter?

When discussing orbital mechanics, you learn that all orbits roughly follow an ellipse which is obtained as the intersection of a cone with an inclined plane, creating conic sections. Below is a ...
8
votes
1answer
488 views

Defy gravity torques with gyroscopes?

Context On the following drawing, a platform is hung from the ceiling not exactly from its centre of gravity. Because of this it can't sustain an arbitrary orientation for long; I want to increase ...
0
votes
1answer
55 views

Calculate orbit height from tangential velocity

Is it possible to calculate the altitude of a satellite orbiting a planet, just from the planet's mass and the satellite's velocity, assuming that the satellite is in a perfect circular orbit? If so, ...
0
votes
0answers
33 views

Can we design the orbit of a satellite with Einstein’s curved space?

I think that the most successful theory of gravity is that the orbit of planet can be explained with this theory and the orbit of satellite was designed with this theory. To design an orbit of a ...
1
vote
3answers
37 views

In this particular problem: Is the mass of the system the mass of the person?

I am doing this problem: The upward normal force exerted by the floor is 620 N on an elevator passenger who weighs 650 N. What is the magnitude of the acceleration? This is how I solved ...
-3
votes
1answer
73 views

Throwing an object in the air [closed]

Studying formulas about velocity and acceleration I came up with a question: if I throw an object in the air with a velocity $v_0$ (suppose i throw it vertically) in how much time its final velocity ...
1
vote
1answer
47 views

Finding at a distance from the Earth speed of satellite [closed]

A satellite at 8000 km from Earth where gravity is 6.4 m/s^2. What is the velocity of satellite? I don't the formula to find speed of satellite.
6
votes
5answers
358 views

Infinities in Newtons law of gravity (for point particles)

Newtons law of gravity for two particles of mass $m_1$ and $m_2$ is: $G\frac{m_1.m_2}{r^2}$. Supposing that the particles are point particles then gravitional attraction will bring them closer ...
1
vote
2answers
112 views

Why does earth have a minimum orbital period?

Using the equation for Kepler's constant for Earth $K$: $$K = \frac{GM}{4\pi^2}$$ $$K = 1.01 \times 10^{13} \;\rm m^3/s^2$$ Finding time ($r = 6.4 \times 10^{6} \;\rm m$ (radius of Earth)): $$K = ...
1
vote
0answers
95 views

Application of trigonometry to the slingshot effect/gravity assist

I have been trying to understand the formula $$v_f^{2}=v_i^{2}+2V(V(1-\cos\beta)+v_i(\cos(\alpha-\beta)-\cos\alpha))$$ as it relates to Fig. 2 on page 5 of this exposition: ...
1
vote
1answer
53 views

Help for orbits of planets

Suppose that an asteroid) that moves at a velocity $v$ passes near to a planet: now I know that the gravity force of the planet will curve the trajectory of the asteroid so I tried to make a draw of ...
5
votes
3answers
396 views

Derivation of Kepler's laws

How can analytically be derived the Kepler's laws? I found some extremely synthetic equations which from the Newton's laws (in particular $\mathbf{F} = m \mathbf{a}$) tried to obtain the Kepler's ...
2
votes
0answers
87 views

Only gravitation and Newton's $2^{\mathrm{nd}}$ law needed to derive Kepler's laws?

It is known that Kepler's laws of planetary motion can be derived from Newton's laws of motion and his law of universal gravitation. However, are all of Newton's laws of motion necessary? According ...
0
votes
1answer
67 views

Tension in string and gravitational force on bob relative strength

When calculating time period of simple pendulum (an approximation of SHM at small amplitudes) we take gravitational force greater than tension in string and resolve gravitational force in two ...
2
votes
3answers
67 views

Question about (complex) motion of Moon

In an ideal situation, we can use a simple formula to determine the velocity at which a body revolves around a massive body at a particular distance. I was wondering if there is an intuitive way to ...
1
vote
1answer
103 views

Tangential and radial acceleration in projectile motion

I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and ...
0
votes
2answers
76 views

Do I need to take weight of the rocket into account when calculating escape velocity?

Here there is the old problem. I know from the old problem that the work $W_v$ that I need to make a rocket fast enough to reach the escape velocity is $$W_v= G \frac{mM}{r}$$ therefore because ...
0
votes
1answer
52 views

Balancing stick on hand - inverted pendulum motion

How do I calculate the velocity and acceleration of a stick that is vertically on my hand? How fast and far do I need to move my hand from side to side to keep balancing the stick? Assuming that we ...