1. Forces, text

2. What is a force?
A push, pull or action

3. What is the unit to measure force?
Newtons and pounds

4. What is weight?
The force of gravity that acts on mass

5. What is the difference between mass and weight?
Mass is the amount of matter something contains (# atoms), so it NEVER changes
Weight will change if the gravity changes, such as between the Earth and the moon

6. What is friction?
A force that resists motion

7. In what direction does friction push?
In the opposite direction of motion

8. What are some different types of friction?
Static, rolling, sliding, air, viscous

9. If something isn’t moving what type of friction is occurring?
Static friction

10. Buoyant force (text 82-3, 86)
Buoyancy is the upward force that a fluid exerts on a submerged object.
It is equal to the weight of fluid that is displaced.
If 10 N of water is displaced, the buoyant force is 10 N
Use a spring scale or graduated cylinder to measure buoyant force (p 83)

11. What can you need to measure to know the exact buoyant force
What can you need to measure to know the exact buoyant force? (text 82-3, 86)
Spring scale or graduated cylinder

12. Net Force

13. The overall force acting on an object is called the
Net force

14. What is the net force when all the forces are balanced?
Equilibrium

15. What happens to motion when the forces are balanced?
Balanced forces do not change motion
If two balanced forces are acting on an object, that object will not change its motion.
If it is still, it will stay still.
If it is moving, it will continue moving, in the same direction and at the same speed.

16. What do you do to find the net force in the picture below?
You add them if they are in the same direction, as shown

17. What is the net force?
300N
350 N
= 650 N

18. What is the net force?
3 N N
3-11
= -8 N

19. Newton’s First Law

20. What do balanced forces do to an object’s motion?
Balanced forces do not change motion
If two balanced forces are acting on an object, that object will not change its motion.
If it is still, it will stay still.
If it is moving, it will continue moving, in the same direction and at the same speed.

21. What is Inertia?
Inertia is the property of an object that resists changes in motion.
Objects with more mass have more inertia and are more resistant to changes in their motion.

22. What would have the most inertia?
Books
School bus
Frog
The school bus because it has the most MASS

23. Newton’s Second Law

24. What is the force needed to move a box with a mass of 50 kg at an acceleration of 2 m/s/s?
F=m x a
F= (50kg) x (2 m/s/s)
100 N

25. Which object would require more force to move because of its mass?
30 kg present
10 kg cake
2 kg hat
30 kg present!

26. What two things affect an object’s acceleration?
Force causes acceleration, and mass resists acceleration.

27. If you are pushing a shopping cart with groceries what could you do to make it go faster?
Add more force (push it harder)

28. Speed

29. How far would Jorge run in 30 minutes at a speed of 5 mi/hr?v T
v= D/T
D=v x T
=5 mi/hr x 0.5 hr
=2.5 mi

30. Using the graph below, what is the speed after 4 seconds?
2.0
1.5
1.0
0.5
1.0 m/s
Speed
Time

31. How would you describe the speed in this graph?
2.0
1.5
1.0
0.5
constant
Speed
Time

32. What is the speed of the object in this graph?10
v= d/t
=10 m/10 s
=1 m/s
Position (m) 10
Time (s)

33. How far did the object move after 5 seconds in this graph?10
D=s x t
=1 m/s x 5 s
=5 m
Position (m) 5 5 10
Time (s)