The description of the movement of bodies by their position, velocity, acceleration (and possibly higher time derivatives, such as, jerk) without concern for the underlying dynamics/forces/causes.

learn more… | top users | synonyms (2)

-1
votes
0answers
32 views

It is possible to have a situiation in which $|\mathrm{d}v/\mathrm{d}t|$ is not zero but $\mathrm{d}|v|/\mathrm{d}t$ is? [on hold]

Please explain the following in detail: It is possible to have a situation in which $\displaystyle\biggl\lvert\frac{\mathrm{d}\vec{v}}{\mathrm{d}t}\biggr\rvert\neq 0$ but ...
0
votes
3answers
44 views

Does a flying bullet get KE from gravity?

A projectile P is shot horizontally at 9.8 m/s from a height of 4.9 m, considering no air friction, after a second it will have v = 9.8 m/s on the x-axis and v = -9.8 on the y-axis. Because of ...
0
votes
1answer
23 views

Minimum turning circle of an accelerating spacecraft

I think I've worked this out, but my maths/physics knowledge is far from perfect, so I'd love confirmation that it is correct. Basically, from $v =\omega r$ and $a_c = v^2 / r$ (where $\omega$ is ...
9
votes
4answers
2k views

Why does the sun make me feel warm?

For a while I thought that the reason I felt warmth from the sun was because my skin was being hit by photons, but then I realized that photons also hit me when I take an X-ray, but I don't feel any ...
-3
votes
0answers
16 views

Kinematics Question: Velocity and Acceleration Polygons [on hold]

I think I've been doing too many of these without much rest because I am stumped. The Curved slider mechanism is what is confusing me: Dimensions of a simple 2-bar linkage are given in the attached ...
-3
votes
0answers
14 views

Kinematics-Motion in 1 dimension [on hold]

A motor car moving at 20m/s can not come to a stop in less than 3s while for a truck this time interval is 5s. On a highway the car is behind the truck both moving at 20m/s. The truck gives a signal ...
-2
votes
0answers
13 views

Kinematics-Motion in one Dimension [on hold]

A man is standing on top of a building 100m high. He throws 2 balls vertically, one at t=0 and the other after a time interval(less than 2s). The later ball is thrown at a velocity of half the first. ...
9
votes
5answers
2k views

If the earth is in constant motion then why do we say that an object is in a state of rest?

I got this question as my physics class homework for tomorrow. Anyone please help me out. If Earth constantly rotates and revolves, then how can we call an object in a state of rest?
0
votes
0answers
41 views

Object pursuing exactly toward an uniformly moving object, with a twist

A friend of mine asked me about a problem he faced in an exam, but I happen to be rusty on this and can't seem to even understand it's implications, nevermind solve it. At $t=0$ an object A in ...
-3
votes
0answers
16 views

Controlling the flow of powder from a container, based on grams selected [on hold]

was wondering how you would control the flow of powder from a container (with a small cylindrical dispenser at the bottom). The container is filled with powder. As the container drains, less ...
3
votes
2answers
139 views

Intepretation of area under velocity-time graph for a bouncing ball

A typical velocity-time graph for a bouncing ball is shown below. I understand that the ball starts from rest at $t=0$, then it accelerates downwards and hits the floor at time $t_1$. Between time ...
0
votes
0answers
27 views

River Boat Problem with a Twist [on hold]

I am trying to solve the following river boat problem . A river of width w is floating such that the stream velocity varies with y as $v_R=v_0(1+(\frac{\sqrt 3 - 1}{w})y)$ where y is the ...
1
vote
2answers
57 views

Projectile motion of Golf ball- Can projection height be calculated just from initial velocity and travel time? [on hold]

A Golf ball projected with a horizontal velocity of 30 meter per second and takes 4 second to reach the ground. Calculate the height the golf ball was projected from. Calculate the magnitude of ...
2
votes
2answers
55 views

Does deceleration (or negative acceleration) feel like acceleration?

This may seem like a dumb question, but I'm having a hard time trying to intuit the answer. The question is in relation to Einstein's famous thought experiment which says that it is impossible for a ...
2
votes
3answers
161 views

Is there an intuitive explanation of the work formula?

Upon learning calculus, I decided it was time to derive all of classical mechanics to give myself a good understanding of physics. What I found was that, while trying to do so, I would need some ...
-1
votes
0answers
12 views

Does driving forward and backward a car with the front wheel bending to the rightmost cause the car to rotate along the same circle? [closed]

When driving a car with the front wheels bent to the rightmost, will the car rotate clockwise along a circle? When driving in the same way except now backward, will the car rotate along the same ...
0
votes
1answer
43 views

Why do systems with a fixed gear-ratio still use gears?

From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is ...
0
votes
4answers
121 views

Why Do Objects move?

Let's imagine a block resting on horizontal table. When We apply a force which is greater than frictional force it moves. But why does this happen? Why can't friction withstand any force? As we know ...
-4
votes
0answers
39 views

Check ym WORK ( average velocity freefall and kinematics [closed]

A car is accelerating in the +x direction at 2seconds the car is 100m from the starting point. after an additional 5 seconds it is 1.5 km from the starting point. a. Determine the average ...
0
votes
3answers
73 views

How can Kinetic energy formula and the Work formula be derived without assuming the other to be true?

After searching how to derive the formula for Kinetic energy, I found that most derivations required the use of the "work" formula. After searching how to derive the work formula for a bit, I found ...
0
votes
0answers
10 views

can I move electromagnetic items in a plane at any direction? [closed]

Lets say we have some balls or other shapes that can be electromagnets (with the relevant electrified coils etc). I want to place stationary electromagnets at the edges of their plane and generate a ...
1
vote
4answers
47 views

Car Crash Scenario [closed]

Two vehicles travelling at 80mph in the same direction. Vehicles are directly behind each other. 12 meter distance between them. Front door of car in front rips of and hits the front window of the ...
0
votes
1answer
49 views

When will the velocity of a particle be perpendicular to it's initial velocity?

I am learning kinematics with vector analysis. I was given the position equation:$\mathbf{r} = 10t\hat{\mathtt{i}} + (20t-5t^2)\hat{\mathtt{j}}$. It asks me the time when the velocity of the particle ...
1
vote
2answers
54 views

Kinematics Question AP Physics [closed]

A motorcycle officer hidden at an intersection observes a car driven by an oblivious driver who ignores a stop sign and continues through the intersection at constant speed. The police officer ...
0
votes
1answer
38 views

Can avg. Vel. be zero in uniformly accelerated straight line motion?

A particle moves in a straight line with constant acceleration. The average velocity of this particle in an interval is zero. According to me it may become possible when velocity of particle is in ...
1
vote
1answer
39 views

Nonzero acceleration is compatible with $d|\vec{v}|/dt=0$; why is the reverse not true?

It is possible to have change in magnitude of velocity w.r.t time to be zero and magnitude of acceleration to be non zero, $$\frac{d|\vec{v}|}{dt}=0 \quad \left| \frac{d\vec{v}}{dt} \right| \neq 0\, ...
14
votes
7answers
3k views

Flat throw vs 45 degree throw of a ball

Why does my sports coach tell me that when I'm fielding I should throw the baseball 'flat' to get the maximum distance? I thought from physics that you get the most distance from throwing at a 45 ...
0
votes
2answers
32 views

Distance traveled from displacement

I am currently reading a book called Physics for Scientists and Engineers by Serway. While reading the chapter about 2-dimensional kinematics, I asked myself a ...
0
votes
2answers
83 views

Convert an equation for acceleration into one for velocity

A sledge is pushed in a straight line. Assume surface is smooth. When the sledge is x distance away from the start the magnitude of its acceleration is given by $0.08e^{-4x}$ and is going in the same ...
0
votes
1answer
36 views

rolling a coin or a riding a bicycle [duplicate]

Why somebody riding a bicycle keeps balance and doesn't fall left or right, while is prone to falling when the bicycle stops. One force (to front) shouldn't affect in any way balance left/right. I ...
0
votes
1answer
68 views

Problem conserving 4-momentum at CoM frame in an inelastic collision [closed]

I am confused about the case where mass is not conserved in a collision (not due to relativistic factors). The center of momentum (CoM) frame is not the same before and after the collision. Let's ...
0
votes
2answers
64 views

Energy in the Relativistic COM Frame

I have been taught that in Classical Mechanics, the total energy of a system of two particles in the Centre of Mass Frame is given by $$ E_\mathrm{total} = \frac{1}{2}MV^2 + \frac{1}{2}\mu v_r^2 $$ ...
0
votes
1answer
30 views

the final velocity non-constant acceleration

I'm not sure if my problem was asked before, but if so, a simple link to the answer would be appreciated. Basically I've recently seen videos about spud cannons that use compressed air and it got me ...
0
votes
3answers
89 views

Difference between $|d{\bf r}|$ and $d|{\bf r}|$

What is the difference between $|d{\bf r}|$ and $d|{\bf r}|$ and why are both of them not always equal to each other? My question might seem stupid to some and will probably get downvoted but I have ...
0
votes
1answer
39 views

Explanation about friction force directions of two moving bodies in contact

can someone explain me why in this scenario (picture below) we have a friction force Ftr12 in the same direction as movement (left part of the picture, case 1 ) and how these directions of friction ...
0
votes
2answers
72 views

Kinetic friction with no force on an object

We've learnt that friction is the opposition of motion and that friction appears the instant a force is applied on an object i.e when an object is at rest (with no force acting on it) then there is no ...
-1
votes
1answer
39 views

For a projectile to cover maximum vertical distance in the least time, what will be the angle of projection? [closed]

My first guess was 90° as there is no horizontal component for velocity when the angle is 90°. But I could not prove it mathematically (and also I'm not sure if it is really 90°).
-3
votes
1answer
38 views

Question to find distance at which 2 trains will pass each other [closed]

I was solving some questions related to motion, and I came through a question which I cant understand. The question goes like this: Two trains A and B, 100 km apart are approaching towards each ...
0
votes
2answers
99 views

Is there a situation where $\left|d\vec{v} / dt\right|$ is non-zero while $d|\vec{v}| / dt$ is zero?

Here $\vec{v}$ represents velocity and $dv / dt$ gives the instantaneous acceleration. $|\vec v|$ gives the magnitude of velocity. When acceleration is zero, then change in magnitude of velocity is ...
0
votes
2answers
88 views

Area under v-t and a-t graphs

I know that the magnitude ( i.e. considering all area as positive) of area under v-t graph gives distance travelled by the particle in the given time. But I've been told that magnitude of area under ...
0
votes
1answer
29 views

Calculate constant acceleration for a length of track with start at rest and final velocity known [closed]

My maths and physics are rusty... I'm a bit ashamed, but I have this problem: Let's have a 1000m linear accelerator (mass driver) propel a payload at constant acceleration, with a final velocity of ...
2
votes
1answer
40 views

Lorentz-invariant phase space of a three-body decay process

I am not following the use of delta function in the 3-body decay process. In $\gamma^* \to gq\bar{q}$ process, with $\gamma^*$ being a virtual photon, we have a phase space factor $$d^9R_3 = ...
9
votes
2answers
735 views

What stops giant cruise ships toppling over in rough seas?

A week ago, 2 of the most gigantic cruise ships in the world docked near my city. If you have seen one, or been on one, you will know how large they are. They look extremely unsafe to me, although ...
-1
votes
3answers
122 views

Isn't a physical frame of reference useless for calculating speed? [closed]

Please ignore relativistic effects and the effects of the expansion of space-time due to the expanding universe theory for the purposes of this question. Whenever someone asks what is the speed of X, ...
4
votes
5answers
448 views

Intuitive answer to a kinematic problem

The problem: Two particles A and B start from rest and move for equal time on a straight line. The particle A has an acceleration a for the first half of the total time and 2a for the second half. ...
0
votes
3answers
67 views

How to apply Newton's first law to moving object?

I'm new to many forces, such as gravity and friction, and I don't really know how they work. I'm trying to simulate a ball bouncing with a program, and it travels at a constant speed horizontally. I ...
1
vote
1answer
31 views

A way to determine if a body accelerates or loses speed at a certain time

With given vectors for acceleration and velocity, is there a way to determine if a body accelerates or decelerates at a certain time-interval? Can this be determined, for instance, by simply observing ...
1
vote
0answers
33 views

irreversibility Aristoteles law of motion

I am watching the second lecture from the theoretical minimum and do not understand the argumentation of Susskind. For those who do not want to watch the video. It is about the law of motion from ...
0
votes
3answers
109 views

Question about rain when an object is moving

So here's the question: A train window is 1 meter high and 10 meters long. A raindrop rolls down the window at a vertical speed of 5 meters per second(when stationary). If the train is moving at 30 ...
9
votes
3answers
1k views

Do you encounter more photons (per unit time) when moving forwards at a constant velocity?

Let's say you have rain hitting you evenly on all sides (not very realistic, I know). If you were to move forwards at a constant speed, there would be more droplets of rain hitting you per second on ...