Newton first law of motion

so what's the main idea behind newton's first law of motion well here's the gist of it an object at rests stays at rest and an object in motion continues in motion unless acted on by a net force that is a non-zero net force so let's illustrate this let's say if i place a block on the ground let's say a five kilogram block and it's at rest that block is going to stay at rest unless you push it if you don't apply a force that block is going to stay where it is however if you apply a force and if that force is strong enough

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the block will begin to slide across that surface and so if you want to cause an object to move it requires an action a force is basically a push or pull action you can push the box to the right or you can pull it with a rope either case a force is required to accelerate the object if no force is applied to the object the object will remain at rest now what about the second part an object in motion continues in motion imagine if imagine a carpet floor and let's say you place a ball on this floor

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and you give it a push so the ball is moving what's gonna happen if you roll a ball against a carpet floor that ball will eventually come to a stop now why is that because newton's first law states that an object in motion continues in motion unless acted on by force why does the ball when it's rolled against a carpet comes to a stop the reason being is there's friction between the ball and between the carpet and so friction is a force that opposes motion friction always causes objects to slow down and

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eventually come to a stop so there is a net force acting on the object and that is its friction now let's say if we can reduce friction so let's say if instead of rolling the ball on a carpet surface let's say if we can take it and give it a push along smooth ice so imagine if there's a lake and it's cold outside it's winter time and the lake freezes over and you take a ball and you roll it against the icy surface what's going to happen to the ball will it come to a stop now going back to the carpet example if

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you roll the ball against the carpet the ball is not going to travel very far it's quickly going to come to a stop it might travel a few meters but it comes to a stop now if you roll the ball against an icy surface it's going to roll for a very very long time it's going to travel a huge distance before coming to a stop now granted there's still friction on the icy surface but that friction is a lot less than what you'll find against the carpet and so that's why the ball is going to travel for a very long time it's going

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to keep going and going and going and eventually after a while it's going to slow down and come to a stop but it's just going to take a long time to come to a stop because the friction that's on the icy surface is a lot less it's still there but it's a lot less let's say you and your friends decide to hang out you decide to go to the bowling alley and it's your turn to roll the bowling ball as you roll it towards the pins whatever direction you roll it to the ball will travel in that direction so let's say

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let me clear this away so let's say this is you and you have the bowling ball in your hand and you're trying to let's say the pins are right here and you have to keep it in this lane you could try to roll it fast or slow but eventually the ball is going to make it to the pins your task is to aim it correctly for instance if you aim the ball this way if you aim it straight you'll notice that the bowling ball will continue to go straight in the direction that you aim it an object in motion will continue in motion unless acted on by

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force so the surface is pretty smooth so friction is reduced to a minimum so the only force that's acting on the ball is the initial push that you give it other than that it just continues in the direction that you sent it now let's say if you stand at an angle that ball will continue to travel in the angle and then you're gonna strike out so you're gonna miss the pins and this is a good illustration that highlights the second part of newton's first law if you roll it towards the left or towards the right you know it's going to

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go straight and reach the edges you're going to miss the pins the only way to get those bowling pins is you have to aim it straight and if you aim it straight it's not going to veer off to the left it's not going to fear off to the right if you realize if you started out straight that ball is going to continue traveling straight it's going to continue in the motion or in the direction that you sent it so you're in control of what direction you sent it now what are some ways in which we can reduce friction altogether

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is there a way that we can eliminate friction because whether you're bowling a ball on a smooth surface or if you're rolling it on an icy surface even though friction even though friction is greatly reduced it's still there so if you roll an object it's not going to continue forever eventually it will come to a stop but can you think of any examples in which friction is so greatly reduced you could say that it's almost a zero one example is space outer space is virtually empty there's hardly any molecules in outer

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space so if you were to throw a ball in outer space that ball will continue to travel unless it encounters another object it's just going to continue traveling straight as long as it's as long as it's not affected by the gravity of a nearby planet or a star that object will continue straight so let's say for example let me clear this away so imagine if you're an astronaut in space and you're pretty far away from earth there's no planets around you no solar systems no stars nothing all there is is just you

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and a ball in your hand now let's say you decide to throw the ball so what's going to happen once you throw the ball to the right the ball is going to travel in the direction that you throw it so if you throw it this way it's gonna travel you're gonna feel something that pushes you back based on newton's third law for every action is an equal and opposite reaction so if you throw the ball to the right you're gonna push back towards the left so as you throw the ball to the right if that ball doesn't encounter an

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asteroid or some other object it's going to continue to travel at the speed that you gave it so it's not going to change direction it's not going to go that way it's simply going to continue in the motion that's set forth by you so it's just going to go straight kind of like that bowling ball example but in space friction is virtually non-existent so that ball will keep on traveling in that direction until it's acted on by net force that is unless it hits or collides with another object or if it enters the gravitational field

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of another planet now let's say eventually it comes next to a planet let's say this is earth then gravity is eventually going to turn this object towards earth and so a net force can change the motion of the object but if there's no net force the ball will continue to travel straight now i want to give you a few situations and i want you to determine if there's a net force acted on an object so let's say ball a is moving straight at constant if ball a moves straight to the right at constant speed

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is there a net force acting on the object the answer is no there is no net force now let's say ball b is moving straight to the right and let's say initially the speed is 20 and then one second later it's 25. so ball b is accelerating is there a net force on the object the answer is yes anytime an object is accelerating or anytime the speed is changing there is a net force now if the speed of the ball changes by five meters per second in one second that means that the acceleration is five meters per second squared

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acceleration is the change in velocity that occurs every second it's how fast the velocity changes every second so if it goes from 20 to 25 in one second the acceleration is five now let's use the third ball ball c now ball c is traveling at constant speed but it's turning at constant speed let's say it's moving at 20 meters per second but it's turning as it does so is there a net force acting on this object now notice that ball c doesn't continue in one direction it's change in direction so anytime an object changes direction

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there is an acceleration that acceleration is perpendicular to the object and the net force is always in the direction of the acceleration so there is a net force so just because the speed is constant doesn't mean the net force is zero the only way the net force is going to be zero is if the object is not moving at all if it's at rest or if it's moving at constant speed in a single direction if the direction changes it's because there's enough force a force causes an object to change its motion

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it can change in two ways the force can cause the object to change its speed it can speed up or slow down or the force can cause the object to change direction when you think of let's say the sun let me use a different color to represent the sun and let's say this is earth earth is relatively small to the sun earth moves relatively at constant speed around the sun for the most part on average however it's constantly changing direction and that's because of gravity the gravitational field that's acting on the earth due to the

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sun causes the earth to move in a circle so the earth moves at constant speed but gravity the gravitational force generated by the sun art that's acted on the earth pulls the earth towards the sun and so instead of the earth just traveling straight towards outer space it turns so keep in mind there's always a force of gravity between two objects the earth also exerts a gravitational force on the sun and these two forces they're equal according to newton's third law of motion for every action force there is

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an equal and opposite reaction force so a force doesn't have to speed up an object or slow it down it can also change the direction of the object yo