# Questions tagged [kinematics]

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.

297 questions
Filter by
Sorted by
Tagged with
171 views

### Circular motion - vectors [closed]

We are asked to show that, if $$\frac{{\rm d} \mathbf{r}}{{\rm d}t} = \mathbf{c}\times\mathbf{r},$$ where $\mathbf c$ is a constant vector, then the body moves in uniform circular motion. I have ...
1k views

### Projectile motion formulas

Assuming: The equations for the vertical and horizontal components of my initial velocity. Are: $v_{x,i} = v_i \cos\theta$ and $v_{y,i} = v_i \sin\theta$ And the displacement components are ...
225 views

### Stellar outflows in the Milky Way

There appears to be a lot of evidence that gas flows outward in Galaxies. I've been trying to parse through the available data and am unable to get a clear answer to this question: is there any ...
2k views

### Finding resultant and direction of resultant

In this question- A motorboat is racing towards north at 25km/h and the water current in that region is 10km/hr in the direction of 60 degree east of south. Find the resultant velocity of the boat. ...
92 views

### When one kid runs into another and they bump heads, why is the slowest mover in most pain? [closed]

In my experience, if one kid runs really fast and accidentally bumps into a second kid who's standing still, and they bump heads, the kid who was 'standing still' (relative to earth) always seems to ...
2k views

### What would happen if an unstoppable force hits an immovable object? [closed]

I realize that the question a rather large paradox, but I do wonder if such a thing were true what would happen, assuming that neither of these "objects" can be destroyed by each other?
1k views

### Could a fish in a sealed ball, move the ball?

If you had a glass ball filled with water, completely sealed and containing a fish, could the fish move the ball?
251 views

### View from a helicopter rotor: why is the horizon distorted?

This video ("rotor panorama") was captured by a camera attached to the rotor head of a radio-controlled helicopter, with the frame rate set to the rotor's frequency. During a long segment of the video,...
2k views

4k views

### What is the origin of the naming convention for position functions?

In physics, position as a function of time is generally called d(t) or s(t). Using "d" is pretty intuitive, however I haven't ...
414 views

### Is $\dfrac{dx}{dt}$ a fraction or not?

I am new to calculus and during my mathematics class my sir defined $\dfrac{dx}{dt}$ as $$dx/dt=\lim_{t\to t_1}\dfrac{f(t)-f(t_1)}{t-t_1}$$ and my sir made a clear statement that $\dfrac{dx}{dt}$ ...
2k views

### How would you move without gravity?

I'm wondering how would you move without gravity? You would still have air pressure at 1Atm. Would you "swim" in the air or would you have do something else?
186 views

### Hypothetical special relativity with mass conservation [closed]

I thought of this question while studying inelastic collisions in special relativity, where kinetic energy is converted into mass-energy. I was wondering if it's possible to formalize a version of ...
1k views

183 views

### Why is the velocity vector perpendicular to the radius vector for projectile motion when the distance from origin is maximal?

After reading this question I have a question of my own: A solution for the furthest distance from the origin for a projectile motion is to solve $(\frac{y}{x}) \cdot (\frac{dy}{dx})=0$. Why is it ...
3k views

### Newton 2nd Law: Does vertical force (mass) affect the horizontal acceleration?

I learnt before that if 2 forces are perpendicular to each other, they should not affect each other. However in a recent experiment setup (asked in another question): I believe the theoratical ...
243 views

### Looking for the curve traced by a moving bicycle when its steering bar is fully rotated

I am looking for a curve traced by a moving bicycle when its steering bar is fully rotated either clockwise or anti-clockwise. How to model it mathematically? Is the curve a circle? My attempt is ...
1k views

### If change in position over time is average velocity, why doesn't change in position over time squared equal average acceleration?

For example, let's say a car is experiencing an acceleration of $1$m/s$^2$, for $6$ seconds so it goes $18$m. Now the average velocity is found through dividing $18$m by $6$s which is in line with the ...
652 views

### The force causing galaxies to accelerate away from each other?

The galaxies in the universe appear to be accelerating away from each other according to the Doppler shift that is present in the light we receive from other galaxies. According to Newtonian ...
968 views

### In perfect vacuum (no external force), if I apply a small amount of force to a body, will it continue to accelerate forever?

According to the equation $F = ma$, the greater the force applied to a body, the greater its acceleration. But in a place where there is no gravity or any other kind of external force, if I apply a ...
2k views

### Why do we care about the difference between speed and velocity?

I teach 7th grade students about the difference between speed and velocity. One of them ask me why do physicists create the concept of velocity. I cannot answer. I don't know precisely why do we care ...
250 views

119 views

### Obtaining a general equation for velocity (in 2D projectile motion)

I'm trying to obtain a general equation for the instantaneous velocity of a projectile moving on a Cartesian plane. I began with the equation for a projectile's trajectory (air resistance neglected): ...
1k views

### Using Kinematic Equations of Motion to find Velocity in Spring-Block System [closed]

Suppose a block of mass, m is connected to a spring of force constant, k. The block is moved on a frictionless surface through distance, b with the help of a uniform external force, F so that the ...