video to understand Newton's 3 laws of motion

Newton invented Calculus to explain motions. 
His most famous equation is referred as Newton’s second law. 

1) Could you find this equation knowing:

- Force (symbol F) causes the velocity  to change from an initial value (Vi) to a final value (Vf) . As the force increases, the change in velocity increases. (∆V = Vf - Vi increases)

-The mass or inertia (m) opposes the change in velocity. As m increases, the change in velocity decreases.

- Increasing the time (∆t) during which the force is applied increases the change in velocity.

Call the change in velocity ∆V . (∆V = Vfinal -Vinitial)

Write: ∆V =  _________________                          Use F, m and ∆t

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The second law is now best known as:
The total force (net force)  acting on a body is equal to the mass times its acceleration
Or F = _________

a is the _____________  , m is the _____________, F is the ______________

a and F are vector quantities. They have magnitude and direction.
But we will only in 1D in 10th grade. We will only consider 2 directions:
 right and left  or up and down. A negative sign shows the down or left direction.
For example: g = -9.8 m/s² means the acceleration due to gravity is pointing down.
Or 1N is the force necessary to accelerate a 1-kg mass at the rate of 1 m/s²
Units for F is newton (of kg m/s/s), units for a is m/s², units for mass is kg.

The other way to write the Newton’s 2nd law helps you understand many situations:

(F ∆T = ∆V /m)

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watch that movie but:
try to answer the questions before he does. Do the experiments.

-  Attach 2 carts by a spring. put 1kg  in one. stretch the spring. mark the middle. the spring exert the same force on both carts. Do the carts get to the middle at the same time ? which one is faster? which one has the smaller intertia ?

- Use a round spring scale. attach a mass of 1kg. Read the weight in Newton. This is the gravitational force exerted by the Earth of the mass. Imagine you are riding inside the mass. (elevator). The mass is accelerated upward. Do you feel heavier or lighter ? F = ma + mg. So your weight seems __________

- same experience but accelerate the mass downward. Would you feel lighter or heavier ? F = mg - ma. Your weight seems ___________.

- If you drop the scale. Imagine you are falling with it. (free-fall). You are now ________________

- Fill a styrofoam cup with water. Make small homes at the bottom. Drop it. (above a sink !). 
The water and the cup are in Free-fall. Does the water leak ?

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2) You increase the speed of a ball you are throwing by keeping it longer in  your hand. Why ?

 

3) According to the second law, if the net force is zero (forces can balance each other), what is the change in velocity ? So what acceleration ?

4) Suppose a high-flying airplane is flying at a constant speed 900km/h and the thrust of the engines is 80,000 newtons. What is the acceleration of the plane ? (hint: change in velocity is .. )Sketch the situation.

5) What kind of relationship you have between the net force and the acceleration?
So if you double the force, you ___________ the acceleration
If you triple the net force acting on a body, you ___________ the acceleration

If you want extra credits and get a better understanding, do graph2  from the menu.

6) A force F is acting on an object of mass m. If you double the mass but keep the force constant
(in magnitude and direction), what will happen to the new change in velocity ∆V?  acceleration?

7) An unbalanced force gives a 2.00kg mass an acceleration of 5.00 m/s². 
What is the force applied to the object ?

8) An unbalanced force of 25N , F, is applied to a 12-kg mass. What is the acceleration of the mass ?

9) A racing car undergoes a uniform acceleration of 8.00 m/s² . If the unbalanced causing the acceleration is 6.00 10³ N . What is the mass of the car ?

 

10) You drag a block of 30g  with a force of 5N  during 10 minutes. What is the change in velocity ?

hint: convert g to kg and minutes to seconds. Use a = change in velocity / change in time

11) You drag a block of 50g with a force of 5N (to the right) .
 A force of friction of 2N is acting to the left.
a) what is the net force ? (right = positive, left = negative)
b) What is the change in velocity of the block after 1 minute ?
hint: use Fnet = m a  and a = change in velocity / change in time.  converte minutes to seconds
and grams to kilograms.
c) What is the change in velocity of the bock after 1 hour ?
d) what is the change of velocity of the block after 1 year ?
e) AFTER 2 YEARS ?
G) if you keep pulling the velocity keeps _______________
h) so can you answer this question:
If one were able to produce and maintain a net force of only 1 Newton on the Queen Mary ocean liner what would be the final speed ?

12) You are pulling on a block with a force of 10N (no friction).
 The block was at rest but reaches a velocity of  5m/s. The time elapsed is 10s .
a) Find the mass of the block.
hint: use F = m (change in velocity / change in time)
b) A friction force of 4N@ left is now acting on the block in addition to the 10N@right.
The motion lasts 3 minutes. i) Find the net force acting on the block. ii)  Find the acceleration.
hint: use the mass found in a). convert minutes to seconds.

13) Albert the skater, 25kg total mass is propelled by a rocket power. The force F exerted by the rocket can vary.
A) Fill the folling table:

force F	acceleration
100N	4 m/s/s
200N
	10m/s/s

B) Suppose now a 50N air resistance force opposes the motion of Albert. F is to the right and the 50N resistance is to the left. Fill the TABLE:

force	acceleration
50N	0 ms/s
100N
200N

16)


A) A ball rolls down a uniform slope ramp. The acceleration is:
decreasing ? constant ? increasing?

If the ramp were steeper, the acceleration would be:
more? the same ? less?

When the ball reaches the bottom and rolls along the smooth level surface it:
continues to accelerate? does not accelerate ?

B)


This time a ball rolls down a ramp of varying slope .   
The ball's acceleration si greater: at the top ? at the middle? at the bottom?

the speed is greater at:

For this case the speed is greater when the acceleration is the : least ? greatest ?

C) can you draw a rampon which the acceleration of the ball will be very little at the top and progressively greater as it moves down the ramp.

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LAB NEWTON's SECOND LAW