Line of compression and tangential force

[rchang72]

A object travelling in a circle does NOT have radial force.

Force gives acceleration. If it had radial force it would go faster or slower around the circle.

Isn't centripetal force a radial force Probably should have said centripetal acceleration to be clearer. I think what you are describing is angular acceleration. But as I said, I'm at least 15 years from my last thoughts about physics.

[Toolish]

Isn't centripetal force a radial force Probably should have said centripetal acceleration to be clearer. I think what you are describing is angular acceleration. But as I said, I'm at least 15 years from my last thoughts about physics.

I am an idiot, I meant tangential force...an object moving in a circle does not have tangential force, as that creates angular acceleration...it does have radial force and acceleration...otherwise it would go straight!

[Mathew]

If the string gets cut the ball flies out in a straight line directly away from the source of the centripetal force that is trying to pull it inwards.

From the website http://www.fearofphysics.com/BallString/ballstring.html

Look at the pictures here

Which way?

The string exerts an inwards force on the ball, called the centripetal force. This is what keeps the ball flying in a circle. When the string is cut, this force vanishes (no more string, no more force). At this point there are no other forces acting on the ball (forget gravity for now). Why are forces so important? Because no object can change its direction unless a force acts on it (this is Newton's First Law).

So what does the ball have after the string is cut? It still has its speed. The speed it had as it was rounding the circle just as the string was cut. This speed is pointing along the edge of the former circle (not outward along where the string used to be.) Without any forces, an object will always go in the direction of its speed (Newton's First Law again).

[Mathew]

I think I have to look at this right from the beginning. I need to look at terminology, so im going to make sure I have these concepts and ill just paste them as I look them up to save anyone else interested the time...

- The line of compression is the direction of the impact force.
- Force is the capacity to do work or cause physical change; energy, strength, or active power.
- A Force is equal to mass times acceleration per newtons 2nd law
- Acceleration is the rate of change of velocity with respect to time.
- Velocity is a vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.
- Vector is a quantity, completely specified by a magnitude and a direction.
- Magnitude is the greatness in significance.

Ok question time relating to these terms....

To maintain a certain velocity of anything, it is always accelerating ?

For a given force when a collision occurs, the force transfered by the acceleration really means the velocity created by that acceleration at that moment in time?

A ball whirling around like in my picture post above - since the velocity or acceleration (discounting the other forces just now) is always tangential to the orbit, then the force of that ball hitting anything (tangential force I assume) is also going to be tangential to its orbit?

and if this is true - then the direction of the clubhead force (keeping the clubface seperate for just now) traveling in its orbit should be tangential to the clubhead orbit?

[Toolish]

I think I have to look at this right from the beginning. I need to look at terminology, so im going to make sure I have these concepts and ill just paste them as I look them up to save anyone else interested the time...

- The line of compression is the direction of the impact force.
- Force is the capacity to do work or cause physical change; energy, strength, or active power.
- A Force is equal to mass times acceleration per newtons 2nd law
- Acceleration is the rate of change of velocity with respect to time.
- Velocity is a vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.
- Vector is a quantity, completely specified by a magnitude and a direction.
- Magnitude is the greatness in significance.

Ok question time relating to these terms....

To maintain a certain velocity of anything, it is always accelerating ?
No...a constant velocity means NO acceleration. Acceleration causes a change in velocity.

For a given force when a collision occurs, the force transfered by the acceleration really means the velocity created by that acceleration at that moment in time?
Force is not transferered by acceleration. Acceleration is created by force. Think of a golf ball dropped from height onto concrete to get an idea of force, accel and velocity. It is released from the hand and at that instant the only force on it becomes gravity (9.8m/s^2), so the ball accelerates down at approximately 9.8m/s^2 (disregarding drag through the air, as it is tiny in this instance), this acceleration continues until the ball hits the ground.

Assume the ball takes 1 second from the time it is released until the time it hits the ground, it will hit the ground at 9.8m/s (velocity). The ground then imparts a force on the ball, accelerating it in an upwards direction. This force and resultant acceleration stops the ball dropping. Due to ball compressing on contact with the ground, when the ball decompresses the upward acceleration continues and the ball ends up with an upward velocity (say m/s). Once impact with the ground is over and the ball is airborne again the only force is gravity and it all repeats

A ball whirling around like in my picture post above - since the velocity or acceleration VELOCITY AND ACCELERATION ARE NOT THE SAME(discounting the other forces just now) is always tangential to the orbitIntantaneous velocity is tangential to the orbit, but acceleration is towards the centre of the orbit. This acceleration is due to the force (tension) in the string, then the force of that ball hitting anything (tangential force I assume) is also going to be tangential to its orbit? The force of the ball hitting anything depends on what it hits and how. Assuming it hits a wall perpendicular to the balls orbit, then yes it will be a tangential force.

and if this is true - then the direction of the clubhead force (keeping the clubface seperate for just now) traveling in its orbit should be tangential to the clubhead orbit?I am confused as to waht you are asking here. The clubhead travelling in an orbit does not have force, it has velocity and momentum. Only once the club is contacts something (hopefully a ball) will it apply a force.

Hope that clears it up a bit?

[Mathew]

Hope that clears it up a bit?

It helps yes

I have to go to bed just now will read it a few more times when I wake up

[neil]

Just one thing, I've read this book and the whole of chapter 2, which surprisingly also includes '2-A resilience' so much I can just about quote it all by memory. When someone says 'it may help to read 2-A' it really bugs the hell out of me...

I actually mean't 2-C-1#3.... it was accidental... I did not mean the lob shot pictures of 2-C-3....

I know the line of flight and the line of compression are seperate. You must take me to be a real idiot or something... That was not what I asked.....

My question is why is the clubhead force going down the angle of approach like in picture 2-C-1#3 instead of off a tangent of the circular clubhead orbit.

Matthew I definately do not think you are an idiot.I was merely responding to your post,which was, I thought, most interesting as this aspect of the book is seldom discussed.I am sorry you took offence as none was meant.I am not trying to make an excuse but originally my post was much longer,but when Itried to preview it ,a note came up saying it was an "invalid thread "or something like that (maybe admin can look into that as it has happened before)I was a little pushed for time so I posted the short thread which does sound a bit condescending in hindsight .I assure you I was only trying to help.

[Mathew]

Matthew I definately do not think you are an idiot.I was merely responding to your post,which was, I thought, most interesting as this aspect of the book is seldom discussed.I am sorry you took offence as none was meant.I am not trying to make an excuse but originally my post was much longer,but when Itried to preview it ,a note came up saying it was an "invalid thread "or something like that (maybe admin can look into that as it has happened before)I was a little pushed for time so I posted the short thread which does sound a bit condescending in hindsight .I assure you I was only trying to help.

Its ok, its probably not just you, I had just woken up also so I was probably 'crabby' mood anyways.

[Mathew]

Anyways looks like my sleep after the nightshift isn't happening so I might ask some questions just now....

I didn't do physics at school past standard grade and just passed that and no more just using common sence and pretty much no study other than knowing speed=distance/time...lol. I was good with maths though which helped some....but im a REAL newbie at this...

To maintain a certain velocity of anything, it is always accelerating ?
No...a constant velocity means NO acceleration. Acceleration causes a change in velocity.

I am very confused with the two. Velocity to me has always been pretty much completely interchangable with speed - is that correct ?

I have always seen it as the faster the speed and the more heavy the weight of an object hitting another object, the more it the second object moves. But with F=ma newtons second law, it confuses me....because it is not the velocity but the acceleration and like you said 'a constant velocity (speed I think...) means no acceleration which results in no force via the equation. If two rocks in space(just to get rid of other forces at the moment) are traveling at a speed or velocity but not accelerating, it appears to me that their should be force applied on to the other. Kinda like if you hit a cue ball in pool and its slowing down to a crawl where it seems to be deaccelerating, it will still give force to the object ball. Im just very confused and I know Im not right here but this is the way im thinking....where am I going wrong ?

[tongzilla]

A Force is equal to mass times acceleration per newtons 2nd law.
To maintain a certain velocity of anything, it is always accelerating ?

Remember it is net force that matters, not any old force. For example, if I am pushing a box forwards on a table at a constant speed, I have to apply force to push it forwards. According to the equation F=ma, there would be acceleration (a=F/m). But because F refers to net force, acceleration is zero. The frictional forces between the table and box cancel out (vector sum of forces equal to zero). When forces are balanced, there is no change in velocity (this does not necessarily mean 0m/s), hence acceleration is zero.

You can maintain a constant speed of something and still make it accelerate, as in circular motion. But you can't maintain a constant velocity.