1. Defining Force Force Newton’s First Law Friction
Motion & Forces
Defining Force
Force
Newton’s First Law
Friction

2. Newton’s First Law
Newton’s First Law of Motion .

3. Force
Force .
What forces are being exerted on the football? 1. 2.

4. Force .
Fkick
Fgrav

5. Force
The force exerted by the players foot is greater than the forces keeping the ball at rest.
Therefore, the resultant force is in the direction of the greater force, the kick.
Fkick
Fgrav

6. Force
Balanced Forces .

7. Force Sometimes it is obvious that a force has been applied.
But other forces aren't as noticeable.
A force can cause the motion of an object to change.

8. Force Fnet Fpull Net Force unbalanced forces – velocity -
What forces are acting on this Cart?

9. DESCRIBE THE FORCES

10. Balanced Forces Net Force –
The net force on the box is zero because ….
Forces on an object that are equal in size and opposite in direction are called….

11. DESCRIBE THE FORCES

12. Unbalanced Forces
When two students are pushing with unequal forces in opposite directions, ……..
NET FORCE- moves the box. .
They are considered to be …..

13. DESCRIBE THE FORCE

14. Unbalanced Forces
The net force that acts on this box is found by …..

15. Newton’s First Law
Newton’s First Law of Motion
. A.K.A. -
Inertia .

16. Inertia and Mass
Inertia is the tendency of an object to resist any change in its motion
If an object is moving, it will have uniform motion.
WHY? .

17. What happens in a crash?
The law of inertia can explain what happens in a car crash.
Explain what happened to this truck.

18. What happens in a crash?
The truck wanted to continue to move forward. The solid object that the truck hit applied a force to the truck that made it stop instantly. As a result, the truck collapsed in on itself
WHAT HAPPENS TO THE PERSON IN THE TRUCK?

19. What happens in a crash? Any passenger …….
Within about 0.02 s (1/50 of a second) after the car stops, unbelted passengers slam into the dashboard, steering wheel, windshield, or the backs of the front seats.
The force needed to slow a person from 50 km/h to zero in 0.1 s is equal to 14 times the force that gravity exerts on the person.

20. What happens in a crash?
How does a seat belt work? - .

21. AIR BAGS Air bags also reduce injuries in car crashes by ….
When impact occurs, a chemical reaction occurs in the air bag that produces nitrogen gas.
The air bag expands rapidly and then deflates just as quickly as the nitrogen gas escapes out of tiny holes in the bag.

22. AIR BAGS
Why is it important that air bags deflate as fast as they expand? .

23. Taken from “The Physics Classroom” © Tom Henderson, 1996-2001.
Concept Test 1
TRUE or FALSE?
The object shown in the diagram must be at rest since there is no net force acting on it.
Answer -
Taken from “The Physics Classroom” © Tom Henderson,

24. Concept Test 2
You are a passenger in a car and not wearing your seat belt.
Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door.
WHAT WOULD HAPPEN TO YOU IN THIS SITUATION?

25. Concept Test 2 Best Answer
1. Before and after the collision, there is a rightward force pushing you into the door.
2. Starting at the time of collision, the door exerts a leftward force on you.
3. both of the above
4. neither of the above