# Tagged Questions

The drag tag has no wiki summary.

1answer
60 views

### In tennis, why does topspin serve bounce higher than flat serve?

When receiving servers (while playing tennis), I've noticed that the tennis ball seems to bounce up higher on me when the server uses a topspin serve than when the server hits a flat serve. Why is ...
2answers
74 views

### How to calculate time for ball to reach plane while considering mass, gravity and wind resistance?

The scenario that I'm having is such that a ball of radius $15mm$ is thrown from a location point $\vec{p}=(2, 5, 2)$ in a direction of $\vec{d}=(3, 0, 4)$. The initial velocity is $30m/s$. There were ...
2answers
115 views

### Could some design of a propeller be used in both air and water?

Propellers in water are smaller in diameter. They also move more slowly. On the other hand, aircraft propellers are larger in diameter, have narrower blades and operate at very high speeds. An ...
3answers
90 views

### Parachute in vacuum

Consider that the earth is vacuum. Consider a person of weight 100 kg is falling from sky with an parachute . He is free falling at height of 3000 m. When will he reach the ground? What would happen ...
0answers
89 views

### Why did increasing the Ackermann geometry in my race car make it faster in corners?

Ackermann geometry is used to account for the different radius arcs that the front tires follow when the steering wheel is turned from center. It's often expressed as a percentage: e.g. 25% Ackermann, ...
1answer
92 views

### Concerning drag on a flow past a cylinder

I am wondering about the drag coefficient for a flow past a cylinder. I am reading this article. I understand why the drag is high to begin with (point 2), when the boundary layer separates and the ...
4answers
467 views

### What causes a soccer ball to follow a curved path?

Soccer players kick the ball in a linear kick, though you find it to turn sideways, not even in one direction. Just mid air it changes that curve's direction. Any physical explanation? Maybe this ...
2answers
234 views

### Explanation that air drag is proportional to speed or square speed?

A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
1answer
152 views

### Drag on a spinning ball in fluid

I am a physics newbie (high school level) and I am wondering what happens when a spherical object is spinning on the spot in a bunch of gas (no gravity here, just an imaginary physics sandbox). Am I ...
2answers
128 views

### Why is simple harmonic motion called so?

Is the motion of a simple pendulum, a simple harmonic motion? It stops vibrating after sometime.
1answer
112 views

### Skiing downhill

The other day on skiing holiday we've been arguing about whether an adult has weight advantage over a child when skiing downhill. I was claiming that gravity is a constant regardless of object's ...
3answers
143 views

### If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?

Of course aerodynamics factors into this question, and the faster you are moving the more air you have to push out of your way, the more energy you use. But would the difference be only a small ...
2answers
180 views

### Forces on an aircraft - thrust, lift, drag, weight

I'm extremely sceptical about the wikipedia page on aircraft flight mechanics. When describing 'straight climbing flight', it says: lift is unable to alter the aircraft's potential energy or ...
1answer
321 views

### Does the metal foam “whiffleball” orbital reentry idea make any sense?

Planetary Resources is a company speaking publicly about mining near Earth asteroids for resources. I'm interested the physicality of a claim they make in a video here: ...
0answers
83 views

### How much force is required to hold an umbrella?

Assuming a small umbrella (e.g. http://www.amazon.com/ShedRain-WindPro-Umbrella-Close-Size/dp/B001DL5WN0). What are the factors that need to be considered? I assume where I hold the umbrella might ...
1answer
143 views

### How would you use the Euler-Lagrange equation to predict the motion of projectiles with linear (Stokes) drag (but no wind)?

My first instinct would be to use the force $$\vec{F} =- \alpha \vec{v}$$ and therefore V(\vec{r}) = \alpha \int_C \vec{v}\cdot d\vec{s} = \alpha \int_C \vec{v}\cdot \vec{v} dt = \alpha \int_C ...
2answers
165 views

### Finding optimal angle for projectile, taking into account linear (Stokes) drag

If you throw a projectile from the ground at a certain angle, it's not hard to see that, assuming we're in a vacuum, throwing it at 45º from the ground will always make it go farthest before it hits ...
2answers
110 views

### Estimating atmospheric friction by measuring the change in velocity of a ball thrown straight upwards

Imagine I throw a ball straight upwards with some velocity $v_1$, and filming the ball with a camera, I can estimate a velocity $v_2$ (along the same vector) after the ball has moved a distance $D$. ...
2answers
328 views

### Work done by the air resistance [closed]

A ball of mass 0.37 kg is thrown upward along the vertical with a initial speed of 14 m / s, and reaches a maximum height of 8.4 m. a) What is the work done by air resistance on the ball? b) ...
1answer
390 views

### Equation for the trajectory of a frisbee?

I'm the lead programmer on a FIRST robotics team, and this year's competition is about throwing Frisbees. I was wondering if there was some sort of "grand unified equation" for Frisbee trajectory that ...
2answers
86 views

### Estimating drag due to wind - ribbon-shaped sail

In the countless calculations and discussions concerning the "space rope" I've never found any addressing its capability to resist winds. Consider, as in most current works, it's a 1m wide ribbon, ...
1answer
127 views

### Is resistance to motion directly proportional to the speed of a moving object?

Power is known to be equal to the force x velocity (P=FV). Im solving a question that states the following : Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s ...
1answer
203 views

### Limitations of drag equation

The magnitude of the air resistance for objects with Reynolds numbers greater than 1000 is given by the formula: Why it does not hold for objects with lower Reynolds numbers? Can I use this ...
2answers
156 views

### Minimum size of an asteroid to actually impact earth

From what I understand, an object entering the atmosphere will start to burn up from the tremendous resistance of the atmosphere. Presumably, for asteroids under a certain size, they will burn up ...
0answers
73 views

### Integration question from book “e: The Story of a Number” by Eli Maor [closed]

In the book 'e: The Story of a Number', a derivation of a parachutist problem is given on pg. 109-110. A parachutist jumps from a plane and at $t=0$ opens his chute. At what speed will he reach the ...
2answers
104 views

### Is air drag equation in term of momentum still valid?

This is the known equation of air drag: $$m{\bf a}=mg-\mathcal D=mg-b{\bf v}.$$ Considering this, is air drag equation in term of momentum still valid? $$m{\bf v}=mv_g-b{\bf r}.$$
4answers
968 views

### Acceleration of two falling objects with identical form and air drag but different masses

I have a theoretical question that has been bugging me and my peers for weeks now - and we have yet to settle on a concrete answer. Imagine two balloons, one is filled with air, one with concrete. ...
1answer
393 views

### Projectile Motion with Air Resistance and Wind

I am wondering how the general kinematics equations would change in the following situation. If an object were fired out of a cannon, or some sort of launcher, so that it had both an initial velocity ...
0answers
129 views

### Torque required to spin a disk along its diameter

How would I calculate (or simulate) this? I am only interested in the aerodynamic drag caused by the surface moving, not any other forces. As far as I know, the only variables needed are the drag ...
2answers
104 views

### What was the muzzle velocity of a home made gun launch strait in the air if air time was 8.2sec?

I built a potato gun and wanted to calculate the muzzle velocity. I remember from physics that I could run the numbers by calculating time from launch until landing. After pointing strait into the air ...
0answers
65 views

### I'm having trouble understanding the dimensions of this falling body problem

I'm working with this: A 50 kg mass is shot from a cannon straight up with an initial velocity of 10m/s off a bridge that is 100 meters above the ground. If air resistance is given by 5v ...
4answers
1k views

### After what speed air friction starts to heat up an object?

I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster. But ...
1answer
125 views

### How much runway does the space shuttle need to land?

A textbook question proposes the following scenario: NASA needs to plan emergency landing sites for the Space Shuttle (RIP). There are a number of things to consider. The shuttle touches down no ...
1answer
227 views

### Finding the diameter a parachute must be to land a probe on Mars at specific speed

Hi I'm trying to solve this textbook example but I don't know where to begin; NASA has decided to send an experimental probe to Mars. Its weight on earth is $40 kg_f$. When the probe is near ...
2answers
116 views

### Kinetic Energy of Stone

If a stone is launched upward, of which is subject to gravity and air resistance, which of the following will have a greater kinetic energy? The stone at a point on its way up, or the stone at the ...
2answers
169 views

### Parabolic motion and air drag

Are this equations correct, in order to calculate the parabolic motion of an arrow with the computation of the drag with the air?  \begin{cases} x(t)=\left(v_0-\frac{1/2C_DA\rho ...
1answer
410 views

### Friction due to air drag at high speeds

I am trying to set up this problem, but I am not sure how to go about doing so. (From University Physics, Young & Freedman): You throw a baseball straight up. The drag force is proportional to ...
1answer
247 views

### How does Baumgartner slow his velocity so that the parachute can open up?

How does Baumgartner slow his velocity so that the parachute can open up? What is Baumgartner's speed just before his parachute opens? What causes his speed to slow down just before the chute opens? ...
6answers
22k views

### Could someone jump from the international space station and live?

Felix Baumgartner just completed his breathtaking free-fall skydiving jump from $120,000\,\text{feet} = 39\,\text{km}$ above the Earth, breaking the speed of sound during the process. I was wondering ...
4answers
2k views

### How Felix Baumgartner has reached the speed of sound quickly

I have watched Felix Baumgartner freefall; but I wonder how Felix has reached the speed of sound quickly, in a matter of some seconds, then we had no idea of its speed? Any explanation please.
1answer
89 views

### Time of a ball going up and down with air resistance

A ball is shot directly upward, and then it comes back to the place where it was shot. Suppose we have air resistance. Suppose $t_1$ is the time period from the moment that the ball was shot to the ...
2answers
181 views

### Does air resistance ever slow a particle down to zero velocity?

If a particle moves in a place with air resistance (but no other forces), will it ever reach a zero velocity in finite time? The air resistance is proportional to some power of velocity - $v^\alpha$, ...
3answers
514 views

### Why would a fat skydiver fall first in free fall?

I was having one of those obnoxious conversations with a friend where he was arguing that a fat skydiver would reach the ground faster than a skinny skydiver. To me it seemed as obvious that the world ...
1answer
156 views

### How can the Air friction force be applied to an object?

Suppose we have an object and we throw it straight upward in the air. How do we apply the Air friction force to this object while moving upwards and after that downwards? Sorry if it's easy because ...
3answers
426 views

### Is it possible to find out the distance traveled by a car if the force applied on it is given?

Say you have car which produces $F$ amount of force which is transferred to the wheels directly. Now assuming that there is air friction which is causing a retarding force proportional to the ...
2answers
1k views

### Equations for an object moving linearly but with air resistance taken into account?

I know (from Kinematics) that for an object moving linearly with an acceleration and without air resistance the following equations can be used to determine v(velocity) or x(position of the object) at ...
2answers
223 views

### Bicycle Wheel Drag in Slipstream

I was recently driving behind a car that had a bicycle mounted on a carrier over the rear bumper. The bicycle wheels were not bound so they were rotating in the slip-stream of the car. I wonder, the ...
1answer
122 views

### What would be an appropiate shape for a parachute?

I'm trying to design a parachute that minimizes the descent velocity, but I'm not sure what shape I should use. From what I've read, ellipse-shaped parachutes are too aerodynamic and minimize drag, ...
2answers
411 views

### Free fall of two spheres made of same materials, different masses, with air resistance

Two people falling with the same parachute will gain different speeds if their masses are different. The upward air drag will needed to be bigger for a heavier person, since gravitational force is ...
2answers
212 views

### At what g is terminal velocity not terminal?

How weak would gravity need to be in order for a human to reliably survive the terminal velocity of falling through air? (Context: watching scifi on a space station with a variety of artificial ...
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