[non]

what's the difference between them? and why is upthrust called reaction?

[Stonebridge]

(Original post by non)
what's the difference between them? and why is upthrust called reaction?

If there is no resultant force on an object there is no acceleration.
For a small "point" mass this is usually referred to as balanced forces.
However, forces can also cause rotation, so "balanced forces" also implies that there is no overall moment or turning effect of the forces.
So I suppose the answer is that most of the time they mean the same thing, but you have to be careful to distinguish between forces that cause linear motion and those that cause rotation.

As for "upthrust", I have never heard that referred commonly to as "reaction". Upthrust is usually the name for the buoyancy force experienced by objects that are immersed in a liquid, for example.
"Reaction" is most commonly used for the Newton's 3rd Law reaction of one object on another, or for the normal reaction of a surface on an object placed on it.

[non]

(Original post by Stonebridge)
If there is no resultant force on an object there is no acceleration.
For a small "point" mass this is usually referred to as balanced forces.
However, forces can also cause rotation, so "balanced forces" also implies that there is no overall moment or turning effect of the forces.
So I suppose the answer is that most of the time they mean the same thing, but you have to be careful to distinguish between forces that cause linear motion and those that cause rotation.

As for "upthrust", I have never heard that referred commonly to as "reaction". Upthrust is usually the name for the buoyancy force experienced by objects that are immersed in a liquid, for example.
"Reaction" is most commonly used for the Newton's 3rd Law reaction of one object on another, or for the normal reaction of a surface on an object placed on it.

thanks but what im meant was that i know no resultant force means its going at a constant speed but does balanced forces mean that as well or does it mean that it's not moving?

also can you help me with a question please.

jo and brian have fitted both their scooters with the same engine. brian and his scooter have a combined mass of 110 kg and an acceleration of 2.80m/s^2. on her scooter, jo only manages an acceleration of 1.71m/s^2

what is combined mass of jo and her scooter?

what forumlae do you use? do you use f=ma?

also, what explains when you walk?
feet push forwards, ground's reaction is upwards?
feet push backwards on ground, ground pushes forward
force in muscles overcomes friction from ground and feet
ground's reaction can't push you backwards because of friction.

i think it's the first option.

[Stonebridge]

(Original post by non)
thanks but what im meant was that i know no resultant force means its going at a constant speed but does balanced forces mean that as well or does it mean that it's not moving?

also can you help me with a question please.

jo and brian have fitted both their scooters with the same engine. brian and his scooter have a combined mass of 110 kg and an acceleration of 2.80m/s^2. on her scooter, jo only manages an acceleration of 1.71m/s^2

what is combined mass of jo and her scooter?

what forumlae do you use? do you use f=ma?

If there is no resultant force on an object it will either be at rest or moving with uniform velocity.

Yes use F=ma
You are given a and m for Brian so find F for the motor.
Use this F (and the given acceleration) for Jo's scooter to find m

[non]

(Original post by Stonebridge)
If there is no resultant force on an object it will either be at rest or moving with uniform velocity.

Yes use F=ma
You are given a and m for Brian so find F for the motor.
Use this F (and the given acceleration) for Jo's scooter to find m

thanks i worked it out and got 177N but isnt that the resultant force not the combined mass and can you help me with:

what explains when you walk?
feet push forwards, ground's reaction is upwards?
feet push backwards on ground, ground pushes forward
force in muscles overcomes friction from ground and feet
ground's reaction can't push you backwards because of friction.

i think it's the first option.

what force is an engine exerting if mass is 2500kg driving force is 2650N. air res is 2000N and friction is 500N

wind is added with force of 200N
calculate its deceleration.

if you know any websites to help with with forces im doing aqa gcse physics and its next week and im really struglling, im using the CGP book, also im getting really anxious because im strugling at physics and think that im going to fail

[non]

(Original post by Stonebridge)
If there is no resultant force on an object it will either be at rest or moving with uniform velocity.

Yes use F=ma
You are given a and m for Brian so find F for the motor.
Use this F (and the given acceleration) for Jo's scooter to find m

please help . im getting really stressed for my exam in a few days.

[Stonebridge]

(Original post by non)
please help . im getting really stressed for my exam in a few days.

Take a look here.
There's A2, AS and GCSE physics notes for AQA
http://www.antonine-education.co.uk/

[Stonebridge]

(Original post by non)
thanks i worked it out and got 177N but isnt that the resultant force not the combined mass and can you help me with:

That's the answer. It's the combined mass in kg as you used the force and acceleration to find it.

what explains when you walk?
feet push forwards, ground's reaction is upwards?
feet push backwards on ground, ground pushes forward
force in muscles overcomes friction from ground and feet
ground's reaction can't push you backwards because of friction.

i think it's the first option.

Is this a real question from the exam board?
It's better to post individual questions in their own thread. That way you will get more replies. These questions will get lost in this thread.

what force is an engine exerting if mass is 2500kg driving force is 2650N. air res is 2000N and friction is 500N

wind is added with force of 200N
calculate its deceleration.

Please post the original question in a separate thread.

if you know any websites to help with with forces im doing aqa gcse physics and its next week and im really struglling, im using the CGP book, also im getting really anxious because im strugling at physics and think that im going to fail

I've posted a good link in my earlier post.

[non]

(Original post by Stonebridge)
Take a look here.
There's A2, AS and GCSE physics notes for AQA
http://www.antonine-education.co.uk/

thanks but i still can't answer my questions, are you able to?

[Stonebridge]

The walking question.
Newton's 3rd Law.
You push back on the ground, the ground pushes forwards on you.
Engine question.
This is not the original question so I can't be sure.
From what you write it looks like
Subtract all the resistance forces from the driving force due to the engine.
This is the resultant force. F
Use F=ma to find "a"

Post original questions in separate threads if you want any more answers.

[non]

(Original post by Stonebridge)
The walking question.
Newton's 3rd Law.
You push back on the ground, the ground pushes forwards on you.
Engine question.
This is not the original question so I can't be sure.
From what you write it looks like
Subtract all the resistance forces from the driving force due to the engine.
This is the resultant force. F
Use F=ma to find "a"

Post original questions in separate threads if you want any more answers.

thanks for your help