4.2 Forces and Motion OCHS

Lesson 4.2

Forces and Motion

Please go to the PHET Force and Motion Basics Simulation in a new tab to use the simulation along with the class

Multiple Choice

Place a small blue person on the left side in the closest spot to the cart, hit START, and observe.

QUESTION

Was the cart in the simulation in equilibrium during this time?

• Yes, Static Equilibrium

• Yes, Dynamic Equilibrium

• No, the object was speeding up

• No, the object was moving with a constant velocity

Draw

Consider only motion after you hit START

Multiple Choice

Hit RETURN . Start with only a small blue person in the first spot again. Hit GO! and count to 3 sec. Then place a small red person on the other side in the same first spot on the rope.

QUESTION:

Is the cart in equilibrium after adding the red person?

• Yes, Static Equilibrium

• Yes, Dynamic Equilibrium

• No, the object was speeding up

• No, The object was moving with constant velocity

Draw

Consider only the portion after you added the red person

WHAT WE KNOW SO FAR...

Constant Velocity - Equilibrium

Changing Velocity - NOT Equilibrium

Multiple Choice

True or False:

If the forces are balanced, then a moving object will slow down and come to rest

• True

• False

Leave the Simulation Paused at this moment while we answer some questions...

​4. Click the right double arrow button to add 50 N of applied force on the system.

Let it run until the speed is about 20m/s and hit [pause]

Draw

Consider only the portion from when you applied the +50N force until you hit PAUSE

Draw

From the Paused moment...

(DO NOT HIT RESET!!)

click the left double arrow button twice so the force is now

—50 N. Press PLAY .

Wait 5-6 seconds to observe the speed of the boxes and hit PAUSE

Multiple Choice

Consider all previous situations...

TRUE or FALSE:

Objects always have to move in the same direction as the net force

• TRUE

• FALSE

Multiple Choice

Consider all previous situations...

TRUE or FALSE:

The direction of Net Force always matches the direction of the Acceleration

• TRUE

• FALSE

WHAT WE KNOW SO FAR...

Constant Velocity - Equilibrium

Changing Velocity - NOT Equilibrium

Acceleration and Net Force Vectors Match

Leave the Simulation Paused at this moment while we answer some questions...

​5. Click the right double arrow button to add 50 N of applied force on the system.

.

THINK: Is this the same as before?

.

Click until the applied force is 400N

Let it run until the speed is about 20m/s and hit [pause]

Draw

Consider only the portion from when you applied the +400N force until you hit PAUSE

​Now hit the back double arrow until the applied force is 200N. Hit PLAY and observe for 2-3 seconds what happens to the velocity now.

Multiple Choice

QUESTION:

How does the rate of change of velocity compare to when you had +400N applied to the boxes?

• The rate of change of velocity was greater for the +200N force

• The rate of change of velocity was greater for the +400N force

• The rate of change of velocity was the same for both forces

• The box had a constant speed in both cases

Draw

Now click the left double arrow button again so the force is now +150 N.

Press play

Wait 5-6 seconds to observe the speed of the boxes and hit pause

Multiple Choice

Consider all previous situations...

TRUE or FALSE:

The direction of Net Force always matches the direction of the Acceleration

• TRUE

• FALSE

Multiple Choice

Consider all previous situations...

TRUE or FALSE:

Objects always have to move in the same direction as the Net Force

• TRUE

• FALSE

WHAT WE KNOW SO FAR...

Constant Velocity - Equilibrium

Changing Velocity - NOT Equilibrium

Acceleration and Net Force Vectors Match

Velocity and Net Force Vectors Don't Need to Match!

Draw

APPLY YOUR UNDERSTANDING:

You are moving to the right in a car. The car suddenly stops and your seat belt tightens against your body.

Consider yourself in the car below...