1. Newton’s Second Law
TEKS 8.6A demonstrate and calculate how unbalanced forces change the speed or direction of an object’s motion
TEKS 8.6C investigate and describe applications of Newton’s law of force and acceleration

2. Net Force, Mass and Acceleration

3. Isaac Newton discovered one of the most important laws of nature; the relationship between net force, mass (inertia) and acceleration.

4. Newton’s Second Law states that the net force acting on a mass causes the mass to accelerate in the direction of the net force.

5. A shorthand way of writing this law is: f = ma
f = force in newtons (N)
m= mass in kilograms (kg)
a = acceleration in meters per second per second (m/s2)

6. Objects with more mass are more difficult to accelerate.

7. If the same force is applied to two objects with different masses, the one with the smaller mass will accelerate more.

8. More mass means less acceleration, unless a larger force is applied.

9. Same Forces small acceleration leads to large acceleration small mass
large mass
large acceleration
Same Forces
small acceleration

10. Different Forces Same Acceleration small force small mass can lead to
large mass
Same Acceleration
small force
large force
Different Forces

11. Falling Objects and Newton’s 2nd Law

12. The Italian physicist and astronomer, Galileo Galilei, studied falling objects.

13. He found that when two objects of different masses are dropped, they fall at the same rate.

14. This was never fully understood until Isaac Newton announced his Second Law of Motion.

15. In the case of free falling objects, the force is equal to the weight of the object, which is determined by the acceleration of gravity (9.8 m/s2).

16. Try dropping a book and a ball of paper. See what happens.

17. Now try dropping a piece of paper and a book.
Most likely you will see that the paper falls more slowly.

18. Remember the book has more weight than the paper, so it has more force to resist friction from the air.

19. Try dropping the book with the paper against
Try dropping the book with the paper against the lower surface of the book.
What happens?

20. Now try dropping the book with the paper on top of the book.
How will the accelerations of the book and the paper compare?
Will they separate
and fall differently?

21. How much force will be required to move the object in each picture?
2 m/s2
m=50kg
f =
m=2000 kg
.05 m/s2 f=
100N
100N
How much force will be required to move the object in each picture?

22. What direction are the forces applied in each picture?
2 m/s2
m=50kg
f =
m=2000 kg
.05 m/s2 f=
right
left

23. No, the rock will accelerate faster.
Will the rock and the van accelerate at the same rate?
No, the rock will accelerate faster.
2 m/s2
m=50kg
f =
m=2000 kg
.05 m/s2 f=