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Newton's Laws

Question

What is the first law?

2 years ago

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18 Replies

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Theresia Reichel

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Issac Newton noticed and was able to show, at the macroscopic levels able to be studied at the time, that objects remain in the same state of motion - UNLESS a resultant force acts upon it.

So if there sum of the resultant force is zero, then:

• a stationary ("resting") object remains stationary (at "rest")

• An object in motion continues to move at the same velocity (It will keep moving at the same speed in the same direction).

However, when the sum resultant force on an object is NOT zero, then the object's state of motion will change.

It will change velocity.

This means it will change speed or direction or speed and direction.

In other words, "the object will accelerate".

It is important to understand that the word "accelerate" in physics doesn't just mean "speed up". It means "change velocity". Velocity is a vector. Velocity has both speed AND direction.

For example, if something is travelling due North at 10ms-1 and is then forced to change direction, say to due East, yet is still travelling at 10ms-, 1 then it still has changed velocity, even though the speed in the new direction is the same speed as the speed in the old direction.

The object is still said to have "accelerated".

(I've found that that this vectorised notion of "acceleration" is often new to students who may struggle with physics and so the terminology can take a little getting used to, at first)

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Sarah N Verified Sherpa Tutor ✓

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Essentially Newtons first law states that an object will keep doing what it was already doing as long as no new force is applied to it.

So it if was moving East at 10m/s then it will keep moving East at 10m/s. It's velocity (speed and direction) remains the same.

If it wasn't moving at all (stationary) then it will remain stationary. Same as above - it's velocity (even though its not moving at all) remains the same.

Once a new force is introduced the resultant force (the force that tells you the direction and by how much) will no longer be zero, so the object will either change the speed or direction it's moving in or start to move if it was stationary.

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Sharanjit Shokar

Newtons First law states that an object will remain stationary/at constant velocity, unless there is a resultant force.

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Object at rest or moving with constant velocity remains so unless a net/resultant external force acts

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Ciaran M Verified Sherpa Tutor ✓

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An object will remain travelling with a constant velocity unless a resultant force acts on the object.

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Mingyang Li

If there is no net force acting on the object, then the object will maintain a constant velocity.

J
Joschka

Newton's first law describes exactly what happens when an object is left to do its own thing - for example, if someone isn't pushing it across the floor. Strictly speaking, this means any time there is no force acting on an object. The best way to imagine Newton's laws is to think about what would happen if an object was in space (because then the added complication of Earth's gravity can be forgotten about). Newton's first law tells us that if no force is acting on an object, then its speed (or technically velocity) won't change - this includes the case where it is not moving at all, and so it will continue to not move. This can be hard to imagine sometimes if you were to picture something on Earth, because on Earth things like friction and air resistance will eventually slow things down. But in space, we can see that an object will just carry on moving forever and ever until something slows it down.

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So in easy terms Newton’s first laws says if you leave an object in the state it is then it will remain in the state forever until unless an external force is applied to it. So Basically it will either remain stationary or it will keep moving at a constant speed. Think of a pen if you leave a pen on a desk, the pen will remain like that forever until or unless something applies a force on it .

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M

Hi Theresia!

The first law states that 'an object will stay at rest, or if it is moving, will stay moving in a straight line until it is acted on by an external force'

In other words an object will keep doing what it is doing until an outside force makes it do something else.

This law is the first law derived by Isaac Newton, who was an English physicist and mathematician.

C
Chippy

Every body continues in its state of rest or state of uniform motion unless it is acted upon by an external unbalanced force

C
Chantal

Newton's first law states that an object in motion will remain at a constant velocity unless an external force acts upon the object. It also states an object will remain at rest unless a external force acts upon the object.

R
Raj Sandhu

the first of newtons laws is inertia, something will not change its state of motion unless an external force acts upon it

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Newton's First Law:

An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force.

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Joseph R Verified Sherpa Tutor ✓

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Assuming you mean Newton's first law of motion, it is: An object will continue its motion unchanged until an external resultant force acts on it.

This basically means, if something's moving at a constant speed it will continue to do so if no new forces act on it. It can also mean if an objects at rest (still), it will continue to be at rest so long as no new forces act on it.

Bonus tip: Objects at rest can and will still have forces acting on them, just the forces will be balanced.

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