1. Describing Force and Motion
***Copy everything on slides 1-7 and then watch the rest of the slides.***

2. 1. What is FORCE and how is it measured?
A push or pull applied to an object
Measured in Newtons (N)
Measured with a spring scale

3. *net force – combination of all forces acting on an object
2. How are forces described?
10N N
Net force = 0
no motion
20N N
Net force = 10N
to the right
20N
10N
Same direction so …
net force = 30 N
Balanced forces – all forces acting on an object are equal
There is NO MOTION
Unbalanced forces – one or more forces acting on an object are stronger than others
There is MOTION

4. 3. What are SPEED and VELOCITY and how are they calculated?
*Speed is the distance an object travels in a unit of time. 50 km/hr
*Velocity is SPEED in a DIRECTION. 50 km/hr west
Sp = d/t
V = d/t include direction
4. What is MOTION?
Occurs when an object changes position relative to a reference point

5. 5. What is Newton’s First Law? (Law of Inertia)
An object at rest stays at rest and an object in motion stays in motion unless acted on by an unbalanced force
Inertia – tendency of an object to resist any change in its motion
Will stay at rest
until force acts
upon it.
Gravity
Will continue
in motion until
these forces or
the wall stops it
Friction

6. 6. What is Newton’s Second Law?
Net force acting on an object causes the object to accelerate in the direction of the force.
6. What is Newton’s Second Law?
Force = mass X acceleration
F = m x a or a = f/m or m = f/a

7. 7. What is Newton’s Third Law?
For every action, there is an equal and opposite reaction.
7. What is Newton’s Third Law?
REACTION
ACTION

8. The truck is in motion. What is the force that causes it to stop?
The push of the stopped car.
The car is at rest. What is the force that causes it to move?
The push of the truck.

9. What about the ladder on top of the truck?
The ladder is in motion because the truck is in motion.
When the truck stops, the ladder stays in motion.
The truck is stopped by the force of the car, but the ladder is not.
What force stops the ladder?
Gravity.

10. The truck is in motion, the car is at rest
The truck is in motion, the car is at rest. How do each of these vehicles accelerate?
The truck stops moving. The car starts moving.
Which one will be the hardest to accelerate?
The truck because it has the most mass.

11. Why does the car move [accelerate] when it is hit by the truck?
The heavy and moving truck has more force than the small, at rest car.
Why does the truck stop moving when it hits the car?
The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck.

12. The truck hits the car. An action force stops the truck.
What is the equal and opposite reaction force?
The force that pushes the car forward.