1. Do Now (2 mins):
Find the horizontal component and the vertical component of this velocity vector
19.0 ms-1
34o

2. Do Now:
A man travels 30 km South, then 20 km West. Draw a vector diagram to show the total displacement of the man.
Josh and Callum are pushing a box. Josh is pushing it with a force of 500 N → and Callum is pushing with a force of 400 N ↑. Draw a vector diagram to show the net force.

3. Do Now:
A bird is flying at 7 ms-1 toward East. The bird changes its direction so it flies at 7 ms-1 toward South.
Draw a vector diagram to show the change in bird’s velocity.

4. “motion under gravity”
Projectile Motion
“motion under gravity”

6. A ball is thrown upwards.
Describe the direction of the ball’s velocity when it is:
going up
going down
at the highest point
Describe the direction of the ball’s acceleration when it is:

7. The only force present on the ball while it is in the air is the weight force. (*Assume that friction is negligible)
Therefore, Fnet = Fweight
and the ball would experience a constant downwards acceleration (9.8 ms-2) the whole time.

8. is called the acceleration due to gravity (= 9.8 ms-2, downwards)
This is the acceleration of any object that is in the air without its own power source (e.g. falling rocks, bullets, shot puts)

9. Try this:
A ball is thrown upwards with an initial speed of 20 ms-1.
How long does the ball take to reach the highest point?
How high does the ball rise?
KUFSS!!

11. Try this:
A ball is thrown upwards. It is airborne for 4.6 seconds before it hits the ground.
What is the initial velocity of the ball?
How high does the ball rise?
KUFSS!!

12. Try this:
A man jumps off a cliff. He falls for 3.4 seconds before he hits the water.
What is his initial velocity?
What is his acceleration?
What is his final velocity (the velocity when he hits the water)?
How high is the cliff?

13. Well…

14. There is NO thrust force or lift force!!!!
Projectile Motion
A projectile is an object that moves through the air without its own source of power. (i.e. the only force is the weight force.)
No wings
No jetpacks
No propellers
There is NO thrust force or lift force!!!!

16. Remember!! There are two motions:
Vertical Motion
Horizontal Motion

17. The bullet question…
A sharpshooter aims and fires his sniper rifle but misses the target  so the bullet just travels horizontally (initially).
How long do you think the bullet will stay in the air (before it hits the ground)?

18. Once in flight, the only force acting on a projectile is its weight force. In this unit, we assume that air resistance is negligible.
This means that:
as the projectile moves, it constantly experiences the downwards acceleration of 9.8 ms-2.
there is no force acting in the horizontal direction, and so the projectile moves horizontally at a constant speed.

19. Projectile Motion = Vertical Motion + Horizontal Motion
In vertical motion:
There is a constant downwards acceleration of 9.8 ms-2 (a = 9.8 ms-2 ↓)
In horizontal motion:
The speed is constant (vi = vf)
There is no acceleration (a = 0 ms-2)

20. Demo – slow motion picture

21. If the car had been travelling faster, would it take longer to fall?

22. The bullet question…
A sharpshooter aims and fires his sniper rifle but misses the target  so the bullet just travels horizontally (initially).
How long do you think the bullet will stay in the air (before it hits the ground)?

23. Demo: falling marble

24. Example:
A marble rolls off a desk and falls onto the floor. The desk is 1.0 m high and the initial velocity of the marble is ?? ms-1 → (horizontal).
Calculate the duration of the fall
During the fall, how far does the marble travel horizontally?

25. Practical – Projectile Prediction 1

26. Textbook Activity 11A
(skip drawing graphs)

28. Try this:
Dan kicks a ball into the air. The initial velocity of the ball is 25 ms-1 at an angle of 42o to the ground.
Calculate the initial horizontal speed
Calculate the initial vertical speed
Calculate the total flight time
Calculate the horizontal distance the ball travels while in the air

29. Remember:
At the maximum height of the flight, the vertical velocity is zero.
Time taken to reach the max height equals the time taken to fall back down
The projectile hits the ground at the same speed as it was fired – but in a different direction!

30. Angle: 61o Initial Speed: 19 ms-1 Calculate: Flight time Range
Maximum height

31. A canon ball is fired into the air at angle of 37o with an initial velocity of 20 ms-1.
Find the horizontal initial velocity.
Find the vertical initial velocity.
For how long would the cannon ball stay in the air?
How far would the cannon ball travel horizontally?

32. A rock is hurled from a catapult.
The initial velocity of the rock is 60 ms-1 at an angle of 50o to the ground.
What would be the total flight time of the rock?
Calculate the maximum height reached by the rock.
Calculate the horizontal distance the rock travels.

34. WORKSHEET SIX
Textbook Activity 11B
Homework Booklet – “Projectile Motion”

35. Practical – Projectile Prediction 2

36. Mr Chu fires a marble straight up into air with his cannon
Mr Chu fires a marble straight up into air with his cannon. The marble stays in the air for ___ seconds. Calculate the initial speed of the marble.
Mr Chu fires the marble at different angles (using the same cannon) as shown in the table. Calculate the flight time and range for each angle.
Angle
Flight Time (sec)
Range (m)
15o
30o
45o
60o
75o

37. Which of these statements are true about projectile motion?
There is only one force, which is the thrust force from the kick/throw/launching/etc.
The weight force is always 9.8 ms-2, downwards.
Acceleration is 9.8 ms-2 and velocity is constant.
The projectile is momentarily “stationary” at the top (max height).
There is zero acceleration at the top.
The projectile ALWAYS accelerates downwards.
The projectile has the same velocity at the beginning and at the end.

38. THEY ARE ALL WRONG
There is only one force, which is the downwards weight force. (Weight force = mg)
The acceleration is always 9.8 ms-2, downwards.
In the vertical motion, there is always an acceleration of 9.8 ms-2 downwards and in the horizontal motion, there is no acceleration and the velocity is constant.
The vertical velocity of the projectile is momentarily “zero” at the top (max height).
In the vertical motion, there is always a downwards acceleration of 9.8 ms-2, even at the top when the velocity is zero.

39. In the vertical motion, when it is moving up, the projectile decelerates at 9.8 ms-2. At the top, the velocity is zero (momentarily). When it is moving down, it accelerates at 9.8 ms-2.
The projectile has the same SPEED at the beginning and at the end, but different directions.