Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?

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If the ball is falling downward, why is the acceleration 9.8 m/s2? If the ball is falling downward, shouldn't the acceleration be increasing?
nope. The velocity is increasing but the acceleration stays the same. That an object accelerates means that it is going faster and faster, but the rate at which it doeas that can be constant. And in the case of gravity on earth it (almost) is.
It doesn't really matter if you use +9.8 m/s/s or 9.8 m/s/s, as long as you're consistent with what you choose. What I mean is that there's no intrinsic reason to say that down is negative and up is positive, or the other way around. Although the general convention is to use down as negative, there's nothing wrong with doing the same problem with down as positive. The only difference is your answers with each method will be opposites of one another. In this case, Sal chose down as negative.
No. Like he says at 2:05, by convention upwards motion = positive, downwards motion = negative. This includes for acceleration. Since gravity always pulls downwards, in this case we have a negative value for acceleration.
I know that the acceleration stays the same, but i was wondering should it be +9.8 m/s2 instead of 9.8 m/s2 since it is falling?
the value of the acceleration is "9.8" because of the Earth gravity. The dimensions are "m/s^2". The "+" or "" in the acceleration depends on your choice of the positive direction. You can solve the same exercise assuming that the positive direction is downwards.In this case the acceleration is + 9.8 m/s^2. Your answer for the final velocity will be the same (same value), but positive.
Because acceleration is a vector quantity, therefore a direction is required. According to convention, () acceleration is used when accelerating downwards (towards the center of the Earth). This acceleration is approximately 9.8m/s/s (slight change in distance from Earth's core is neglected), this doesn't change but it impacts the velocity. In short, the () only indicates the direction, and when the ball is travelling in that direction (downwards) it accelerates which in Sal's case results in a negative velocity. BTW, good question!!
it doesnt matter whether the body is rising or falling,it is always negative because of acceleration being a vector quantity,check the october /november 2011 cambridge paper 1,marking scheme question number 18,thank you,,
no because the acceleration is assumed constant and if it is constant that means it stays the same the velocity does increase though because the acceleration adds on and on and on till it hits something.
Why in same type of questions in one velocity is+20m/s and in 2nd question it is 20m/s
If acceleration is 9.8m/s2 that only means velocity is decreasing. Isn't it?
Example: my initial velocity = 98 m/s and final velocity= 0 m/s within 10 sec. What is my deceleration (or negative acceleration)?
Ans: 9.8 m/s2
Which means, by the time object reaches earth velocity will decrease? But that isn't the case.
Example: my initial velocity = 98 m/s and final velocity= 0 m/s within 10 sec. What is my deceleration (or negative acceleration)?
Ans: 9.8 m/s2
Which means, by the time object reaches earth velocity will decrease? But that isn't the case.
I still have a doubt about the same.....
Not understood why we really take negative acceleration when a body is falling downwards...Shouldn't the acceleration be increasing....?
Not understood why we really take negative acceleration when a body is falling downwards...Shouldn't the acceleration be increasing....?
according to the direction of the motion
.....the +ve direction is upward .... the ve direction is downward ........ the acceleration in this quest lies in the ve direction
.....the +ve direction is upward .... the ve direction is downward ........ the acceleration in this quest lies in the ve direction
you were wrong because it increases when it goes up
At 2:05 Sal says "A positive Vector means up, and a negative vector means down" So if the velocity is negative it means that the rock is going down. I hope this helps, but it seems that I am five years late :(
Actually, accelaration is becoming smaller, because air resitance eventually takes effect. There is a point where there is no more accelaration, because air resistance and gravity accelaration are exactly opposite, so they cancel out, so then there is no more accelaration
The MAGNITUDE of the acceleration is increasing all right. But you have to remember that acceleration is a vector quantity, and vector quantities consist of magnitude as well as direction. And once, in the video, it was mentioned that 'up' is positive, and 'down' is negative. Since the object accelerating due to free fall is falling down, it is denoted with a '' sign.
acceleration is constant in this case, its neither increasing nor decreasing, the minus sign used here denotes the direction only, i.e. downward.
no as sal took above positive and downwards negative so a is negative.
if he would have taken above negative and downwards positive then a would be positive which will not effect the answer
if he would have taken above negative and downwards positive then a would be positive which will not effect the answer
At 2:06 Sal said up is positive and down is negative.
velocity is still increasing but negative just signifies the direction
The + or  sign in the acceleration denotes the orientation or direction.. In the case stated by Sal, we assumed that going up is + while goind down is .. since it is going down the acceleration is negative.
It doesn't really matter if you use +9.8 m/s/s or 9.8 m/s/s, as long as you're consistent with what you choose. What I mean is that there's no intrinsic reason to say that down is negative and up is positive, or the other way around. Although the general convention is to use down as negative, there's nothing wrong with doing the same problem with down as positive. The only difference is your answers with each method will be opposites of one another. In this case, Sal chose down as negative by a
Main reason is that velocity is used which is a vector that includes direction, it would be correct to say the speed (which ignores the direction) is positive, in the example shown the speed = approx 9.9 m/s
Thanks
Do heavier or light objects fall faster when thrown from a height
the negative sign here refers to the direction. it does not matter if it increases or not. and there is another thing the velocity of the object increses bu the the acceleration remain the same because it is the rate of increasing in velocity not the velocity itself
The ball is accelerating down wards so it is 9.8m/s^2, but it is still getting faster
I think its only the direction that you specified to gravity for a given frame according to the question and .. if you have suggested the direction as + or  then you must continue to solve the question with respect to that specified direction of gravity only either the object is moving upwards or downwards.
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