1. Forces and Motion PS9.21 PS9.22 PS9.23 PS9.24 ps9.25

2. Forces can create changes in motion 3 types of acceleration (change in speed or direction
(acceleration) speeding up
Deceleration is negative acceleration or slowing down
Centripetal acceleration changing direction

3. Motion can be described as
a change in an object’s position
Average velocity (speed) is the change of position of an object over time

4. Velocity Graphs V = distance time
Velocity (v) is the slope (rise over run) of a position (d) vs. time (t) graph

5. 40 The diagram represents the total travel of a teacher on a Saturday
40 The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed?
F Q
G R
H S
J T
How do we work this one?
Calculate v = d/t for each segment.

6. Acceleration Graphs
Acceleration (a) is the slope of a velocity (v) vs. time (t) graph
Plotted on a distance vs. time graph, acceleration is an exponential curve

7. Acceleration is a change in an objects velocity (speed or direction)
When an object’s speed changes over time it is accelerating (or decelerating)
A = vfinal – vinitial
time
Units for acceleration m/s/s or m/s2

8. Definition of a Force
A Force is a push or a pull

9. Balanced Force
A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.
If you were to add these forces they would = 0

10. Unbalanced Forces
Are forces that results in an object’s motion being changed. +
Add together to equal greater force.

11. Friction
A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

12. Friction Friction causes an object to slow down and stop.
Since the amount of energy stays constant, the energy becomes heat.
Air resistance is an another example of friction.
Lubricants or grease reduce friction.

13. Newton’s 1st Law of Motion
Object in motion stays in motion

14. Newton’s 1st Law of Motion
And Objects at rest stay at rest

15. Newton’s 1st Law of Motion
Until they are acted upon by unbalanced forces.

16. Inertia or Newtons 1st Law
Tendency for an object to stay at rest or moving in a straight line at a constant speed.
The mass (m measured in kg) of an object determines its inertia
Inertia comes from the Latin word meaning lazy.

17. Newton’s 2nd Law of Motion
Force = Mass X Acceleration
F=ma
Weight (pull of gravity) is a
commonly measured force, calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2

18. Newton’s 2nd Law of Motion
The greater the mass of an object, the greater the force required to change its motion.

19. Newton’s 2nd Law of Motion
The greater the acceleration of an object, the greater the force required to change its motion.

20. Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2.
11 The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping?
A 0.2 N
B 0.8 N
C 1.5 N
D 6.0 N
Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2.
So, .5 kg x 3 m/s2= 1.5 N

21. Newton’s 3rd Law of Motion
For every action force there is an equal and opposite reaction force.

22. Newton’s 3rd Law of Motion
All forces come in action-reaction pairs
Ex: feet push backward on floor, the floor pushes forward on feet

23. Universal Law of Gravitation
Between any two objects in space there is gravity

24. Universal Law of Gravitation
Gravity varies depending on two factors:
1) the mass of the object doing the pulling, and
2) the distance from the center of that object

25. On Earth gravity = 9.8 m/s/s
For every second that an object falls its speed increases by 9.8 m/s