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Feedback Comments on Motion

by Ron Kurtus

A total of 228 comments and questions have been sent in. They are listed according to date.

List of next 10 letters




Motion Projecting object upward Kenya
Motion Laws Force in the opposite direciton India
Pendulum Want pendulum formulae India
Motion Jumping frogs problem India
Motion Why is motion relative? India
Motion Throwing object straight up UAE
Periodic Motion Difference between harmonic and periodic motion India
Pendulum Doing investigation with double pendulum UK
Pendulum What would happen if a Foucault Pendulum didn't swing? USA
Motion What is acceleration? India

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First 10 letters

Projecting object upward

Topic: Motion


October 5, 2010

a body is projected verticaly upwards under gravity at28m/s,how long will it take to reach 300m.

Daniel - Kenya



See "Gravity Time Equations for Objects Projected Upward" at:

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Force in the opposite direciton

Topic: Motion Laws


October 4, 2010

According to newton's third law ,when we apply a force by pushing a substance ,we are applying energy to the substance and in reaction the substance will also apply a force toward us.So,the question is that ,from where the substance find the energy to reply our it reflecting our energy or anything else....?

Rrg - India



Inertia is a property of matter where the object will tend to stay in one place if it is not moving, as well as continue in a straight line if it is moving.

When you apply a force to an object you are overcoming its inertia, which then causes a resistance to your force. This resistance is not a real force in the opposite direction. Instead, it is called a virtual or pseudo force.

Many textbooks mistakenly imply it is an actual force coming from someplace.

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Want pendulum formulae

Topic: Pendulum


September 24, 2010

I want all formulae related to pendulum and animations of the concepts of pendulum to make it more clear




See "Simple Pendulum Equations" at for the equations and formulae.

The pendulum lesson has the animation.

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Jumping frogs problem

Topic: Motion


July 31, 2010

Two frogs start hopping towards each other,starting from a distance of D.Frog 1 hops at a speed that is 25% faster than that frog 2.At what distance(as measured from where frog1 started) will they meet?

krishna - India



D = D1 + D2
D1 = vt
D2 = 1.25vt
D = 2.25vt
Frog 2 will travel 1.25D/2.25 = 0.55D

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Why is motion relative?

Topic: Motion


July 29, 2010

Why is motion relative

Aditya - India



If you change positions or move, it must be with respect to some other object. Even when you walk, you are moving with respect to the ground. That is what is called relative motion.

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Throwing object straight up

Topic: Motion


July 23, 2010

if abody is thrown straiht vertically upwards,
A,how much time does it take to reach at its maximum
A,height?(take g=10m/s2

B,what is the maximum height traveled by the body?

frehiwot - UAE



See our lesson on "Gravity Time Equations for Objects Projected Upward" at:

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Difference between harmonic and periodic motion

Topic: Periodic Motion


July 22, 2010

what is Harmonic motion and what is periodic motion?

Kranthi - India



Periodic motion is when an object continually moves back and forth. However, that motion can be driven--such as a being powered by a motor--or it can be damped, like back and forth motion in a liquid.

Simple harmonic motion is pure periodic motion, where nothing is driving or damping the motion.

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Doing investigation with double pendulum

Topic: Pendulum


July 16, 2010

Hi there,

My name is Tony, and I am an A-level student, studing at Carisbrooke High School. For my Physics course I have to conduct a Long investigation piece of coursework. For this I am taking data from a pendulum experiment and using Calculus and Trigonometry to mathematically model a pendulum within a real world environment.

My problem is I need a real situation which would motivate me to conduct such an investigation. The experiment I am going to do involes a 2 meter long pendulum with a 500 gram mass,and a fix beam (with damping effects) 1.75 meters from the top of the pendulum (fulcrum point A), creating another fulcrum point(fulcrum point B). This means when the pendulem passes the centre line of gravity it encounters the beam, shifting the fulcrum from point A to point B and therefore changing the lenght of the pendulm giving it a faster period at T/4
I was wondering whether you knew of any real life examples where this would happen which could give me a situation to do this experiment as a part an investigation.



Antony - UK



It looks like your configuration is a simple version of a double pendulum, which is one pendulum connected to another. Information, equations and animations of such a pendulum can be seen at:

Some of the solutions for such a pendulum involve Chaos Theory.

One use for your pendulum would be the capability to readily tune the frequency by sliding the second beam or fulcrum B up or down. If the pendulum was used as part of a clock, the movement of the fulcrum could be used to maintain accuracy.

I hope this helps. Best wishes in your investigation. Let me know how things turn out.

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What would happen if a Foucault Pendulum didn't swing?

Topic: Pendulum


July 12, 2010

What would the relative movement of a pendulum to the Earth be if the pendulum's bob were still? Say, for example, the weight of a Foucault Pendulum were slowed to stop. Would the weight keep its position relative to the ground(Earth), or would it appear to circle(arc) slowly and slightly around a point or axis while the Earth rotated beneath it?




If you put a Foucault pendulum at the geographical north pole, it would maintain its direction of swing as the Earth turned under it, due to the conservation of momentum in a given direction. If the pendulum was not swinging, it would have zero momentum in any direction.

However, if the pendulum was at some other position on the surface of the Earth, would the rotation of the Earth cause the pendulum to move slightly? I think it might want to move, but the force would be much less than needed to overcome inertia.

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What is acceleration?

Topic: Motion


July 8, 2010

Hi,,,,This is absolutely a good class. Explain me about acceleration,for better understanding with also some example.

And plz send me your name, country, email.

Anil - India



Acceleration is the rate that velocity increases. You divide the velocity increase by the time it takes to reach the new velocity to calculate the acceleration.

We are located in the United States.

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