do now!
DESCRIPTION
Do now!. Hey dudes, c an you go through your folders and make sure everything is in order?. Newton’s Laws of Motion. That’s me!. Newton’s 1 st Law. An object continues in uniform motion in a straight line or at rest unless a resultant external force acts. Newton’s 1 st Law. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/1.jpg)
Do now!Hey dudes, can
you go through your folders and make sure everything is in order?
![Page 2: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/2.jpg)
Newton’s Laws of Motion
That’s me!
![Page 3: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/3.jpg)
Newton’s 1st Law
An object continues in uniform motion in a straight line or at rest unless a resultant external force acts
![Page 4: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/4.jpg)
Newton’s 1st Law
An object continues in uniform motion in a straight line or at rest unless a resultant external force acts
Does this make sense?
![Page 5: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/5.jpg)
Newton’s 1st law
Newton’s first law was actually discovered by Galileo.
Newton nicked it!
![Page 6: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/6.jpg)
Newton’s first law
Galileo imagined a marble rolling in a very smooth (i.e. no friction) bowl.
![Page 7: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/7.jpg)
Newton’s first lawIf you let go of the ball, it always rolls up the opposite side until it reaches its original height (this actually comes from the conservation of energy).
![Page 8: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/8.jpg)
Newton’s first lawNo matter how long the bowl, this always happens
![Page 9: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/9.jpg)
Newton’s first lawNo matter how long the bowl, this always happens.
constant velocity
![Page 10: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/10.jpg)
Newton’s first lawGalileo imagined an infinitely long bowl where the ball never reaches the other side!
![Page 11: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/11.jpg)
Newton’s first lawThe ball travels with constant velocity until its reaches the other side (which it never does!).Galileo realised that this was the natural state of objects when no (resultant ) forces act.
constant velocity
![Page 12: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/12.jpg)
Other examples
Imagine a (giant) dog falling from a tall building
![Page 13: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/13.jpg)
Other examples
To start the dog is travelling slowly. The main force on the dog is gravity, with a little air resistance
gravity
Air resistance
![Page 14: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/14.jpg)
Other examples
As the dog falls faster, the air resistance increases (note that its weight (force of gravity) stays the same)
gravity
Air resistance
![Page 15: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/15.jpg)
Other examples
Eventually the air resistance grows until it equals the force of gravity. At this time the dog travels with constant velocity (called its terminal velocity)
gravity
Air resistance
![Page 16: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/16.jpg)
Oooops!
![Page 17: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/17.jpg)
Another example
Imagine Mr Porter cycling at constant velocity.
![Page 18: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/18.jpg)
Newton’s 1st law
He is providing a pushing force.
Constant velocity
![Page 19: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/19.jpg)
Newton’s 1st law
There is an equal and opposite friction force.
Constant velocity
Pushing force
friction
![Page 20: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/20.jpg)
Newton’s second law
Newton’s second law concerns examples where there is a resultant force.
I thought of this law myself!
![Page 21: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/21.jpg)
Let’s go back to Mr Porter on his bike.
Remember when the forces are balanced (no resultant force) he travels at constant velocity.
Constant velocity
Pushing force
friction
![Page 22: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/22.jpg)
Newton’s 2nd law
Now lets imagine what happens if he pedals faster.
Pushing force
friction
![Page 23: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/23.jpg)
Newton’s 2nd law
His velocity changes (goes faster). He accelerates!
Pushing force
friction
acceleration
Remember from last year that acceleration is rate of change of velocity. In other words
acceleration = (change in velocity)/time
![Page 24: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/24.jpg)
Newton’s 2nd law
Now imagine what happens if he stops pedalling.
friction
![Page 25: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/25.jpg)
Newton’s 2nd law
He slows down (decellerates). This is a negative acceleration.
friction
![Page 26: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/26.jpg)
Newton’s 2nd law
So when there is a resultant force, an object accelerates (changes velocity)
Pushing force
friction
Mr Porter’s Porche
![Page 27: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/27.jpg)
Newton’s 2nd law
There is a mathematical relationship between the resultant force and acceleration.
Resultant force (N) = mass (kg) x acceleration (m/s2)
FR = maIt’s physics,
there’s always a mathematical relationship!
![Page 28: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/28.jpg)
An example
What will be Mr Poter’s acceleration?
Pushing force (100 N)
Friction (60 N)
Mass of Mr Porter and bike = 100 kg
![Page 29: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/29.jpg)
An example
Resultant force = 100 – 60 = 40 NFR = ma
40 = 100aa = 0.4 m/s2
Pushing force (100 N)
Friction (60 N)
Mass of Mr Porter and bike = 100 kg
![Page 30: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/30.jpg)
Newton’s 3rd lawIf a body A exerts a force on body B, body B will exert an equal but opposite force on body A.
Hand (body A) exerts force on table (body B)
Table (body B) exerts force on hand (body A)
![Page 31: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/31.jpg)
Don’t worry!
We’ll do more on Newton’s 3rd law next week.
![Page 32: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/32.jpg)
Free-body diagrams
![Page 33: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/33.jpg)
Free-body diagrams
Shows the magnitude and direction of all forces acting on a single body
The diagram shows the body only and the forces acting on it.
![Page 34: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/34.jpg)
Examples
• Mass hanging on a rope
W (weight)
T (tension in rope)
![Page 35: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/35.jpg)
Examples
• Inclined slope
W (weight)
R (normal reaction force)
F (friction)
If a body touches another body there is a force of reaction or contact force. The force is perpendicular to the body exerting the force
![Page 36: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/36.jpg)
Examples
• String over a pulley
T (tension in rope)
T (tension in rope)
W1
W1
![Page 37: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/37.jpg)
Examples
• Ladder leaning against a wall
R
R
F
F
W
![Page 38: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/38.jpg)
Resolving vectors into components
![Page 39: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/39.jpg)
Resolving vectors into components
It is sometime useful to split vectors into perpendicular components
![Page 40: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/40.jpg)
Resolving vectors into components
![Page 41: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/41.jpg)
A cable car question
![Page 42: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/42.jpg)
Tension in the cables?
10 000 N
?? 10°
![Page 43: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/43.jpg)
Vertically 10 000 = 2 X ? X sin10°
10 000 N
?? 10°
? X sin10° ? X sin10°
![Page 44: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/44.jpg)
Vertically 10 000/2xsin10° = ?
10 000 N
?? 10°
? X sin10° ? X sin10°
![Page 45: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/45.jpg)
? = 28 800 N
10 000 N
?? 10°
? X sin10° ? X sin10°
![Page 46: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/46.jpg)
What happens as the angle deceases?
10 000 N
?? θ? = 10 000/2xsinθ
![Page 47: Do now!](https://reader035.vdocument.in/reader035/viewer/2022070423/56816793550346895ddcce0d/html5/thumbnails/47.jpg)
Let’s try some questions!
Page 67 Question 2Page 68 Questions 6, 8, 10.Page 73 Questions 3, 4, 5
Page 74 Question 9, 12Page 75 Question 14
Page 84 Questions 2, 3, 4, 5, 6, 8, 9
Page 85 Questions 13, 16, 20, 21.