Part B: Newton's 2^nd law of motion

1. Acceleration and Force

*Open the PhEt simulation first https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

1) Select "Motion" section on the bottom of the simulation.

2) Check all the check boxes for Sum of Forces, Values, and Speed.

3) Using a stopwatch or timer on your phone, Measure how long it takes to reach speed of 40 m/s when a crate is pushed by a 100N, 200N, 300N, 400N, and 500N force (you can add 50N by clicking fast forward icon() once). Note: there's no friction force in this section of simulation.

4) Once you have tested with a force, reset () and repeat 3) with a different force.

5) Then, complete the data table below with times and calculated accelerations.

Name of Object: Crate Mass (kg): 50 kg *the first row in the table is an example.(

Force	Time (s)	Acceleration measured (m/s2)	Acceleration by F/m (m/s2)
100N	20.5 seconds	a = Vf - Vi = 40 m/s - 0m/s t ( 20.5 ) s = ( 1.95 ) m/s2	a = 100N / 50kg = 2 m/s2
200N		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
300N		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
400N		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
500N		a = 40 m/s - 0m/s ( ) s = ( ) m/s2

2. Acceleration and Mass

*Open the PhET simulation first https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

1) Select "Motion" section on the bottom of the simulation.

2) Check all the check boxes for Sum of Forces, Values, and Speed.

3) Using a stopwatch on your phone, measure how long it takes to reach speed of 40 m/s when each object is pushed by a force of 100N. Then, calculate the acceleration of the object using the time measured. When you finish, you should be able to know the mass of the mystery object.

4) Then, complete the data table below. (Applied force: 100N)

Object	Mass (kg)	Time (s)	Acceleration (m/s2)	Acceleration by F/m (m/s2)
Child	40 kg	15.7 s	a = Vf - Vi = 40 m/s - 0m/s t ( 15.7 ) s = (2.55) m/s2	a = 100N / 40kg = 2.5 m/s2
Box	50 kg		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
Adult	80 kg		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
Trash can	100 kg		a = 40 m/s - 0m/s ( ) s = ( ) m/s2
Mystery item (What is its mass?)	( ) kg		a = 40 m/s - 0m/s ( ) s = ( ) m/s2

Part C: Friction

*Open the PhEt simulation first https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

1) Select "Friction" section on the bottom of the simulation.

2) Check all the check boxes for Forces, Sum of Forces, Values, Masses, and Speed.

3) Find out the friction forces on each object when it is pushed by 50 N or 100 N.

3) Click reset () button after you have tested each object.

1.Friction force when an object is not moving

With the friction bar set in the middle, find the friction force on each object when applied force is 50N or 100N (but when it is not moving).

Object	Mass (kg)	Applied Force (N)	Friction Force (N)	Sum of Forces or Net Force (N)
Child	40 kg	50 N	50 N	0 N
100 N	100 N	0 N
Box	50kg	50 N
100 N
Adult	80kg	50 N
100 N
Trash can		50 N
100 N
Refrigerator		50 N
100 N

2.Friction force when an object is moving

*Open the PhEt simulation first https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

1) Select "Friction" section on the bottom of the simulation.

2) Check all the check boxes for Forces, Sum of Forces, Values, Masses, and Speed.

3) Increase or decrease the applied force on the object using fast forward (50 N) or play (1 N) buttons to find out the forces asked in the table below.

4) Click reset () button after you have tested each object.

Object	Applied Force (N) needed to cause the object to begin moving	Sum of Forces (Net Force to the right) while it is speeding up	Frictional Force (N) Acting on the Object once it starts moving	Minimum Applied Force (N) needed keep it moving at a constant velocity once it starts moving	Sum of Forces (Net Force) needed to keep object moving at a constant velocity once it starts moving
Child (40 kg)	101 N	26 N	75 N	75 N	0 N
Crate (50 kg)
Adult (80 kg)
Trash can (100 kg)