P0998900
Force and reaction
Physics
Mechanics


Forces, work, power & energy


Difficulty level
Group size
Preparation time
Execution time
easy
2
10 minutes
10 minutes
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Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Teacher information
Application
1. With the help of spring balances, the students
are to learn that a force can only be exerted
on a body if a counterforce acts on this body
at the same time.
2. By means of two spring balances, the
students are to work out experimentally that
the forces on both spring balances are
equally strong, i.e. force = counterforce (actio
= reactio).
Experimental setup
2/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Other teacher information
Prior
knowledge
It is assumed that the students have carried out the experiment " Measurement of
forces" and understood the physical relationships.
The SI unit of force F is a Newton N :
1 N = 1 kg ⋅
Scientific
Principle
m
s2
Forces always occur in pairs. If a body A exerts a force on another body B (actio), a
force of the same magnitude but opposite direction is exerted by body B on body A
(reactio).
Other teacher information
Prior
knowledge
It is assumed that the students have carried out the experiment " Measurement of
forces" and understood the physical relationships.
The SI unit of force F is a Newton N :
1 N = 1 kg ⋅
Scientific
Principle
m
s2
Forces always occur in pairs. If a body A exerts a force on another body B (actio), a
force of the same magnitude but opposite direction is exerted by body B on body A
(reactio).
3/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Other teacher information (2/2)
Learning
objective
Tasks
The students should get a feeling for the position dependence and adjustment of spring
balances. In addition, the students learn about the principle of counterforce.
Two spring balances are connected together and the forces they exert on each other
are measured.
Safety Instructions
The general instructions for safe experimentation in science lessons to be applied to
this experiment.
4/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Student Information
Motivation
No matter whether during the launch of a
rocket at a spaceport, the forward motion of an
aircraft in the air or the start of a sprinter at the
launch pad: the forward motion is only
generated by generating an equally large force
in the opposite direction. In the case of a rocket
launch, this is the ejection of the fuel gases after
combustion, which thereby generate a forward
thrust sufficient for the rocket to overcome the
earth's gravity.
In this experiment you learn that every force
produces a counterforce.
Rocket Launch
5/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Material
Position
1
2
3
4
5
6
Material
Item No.
02001-00
02036-01
02037-00
03065-02
03065-03
03065-20
Support base, variable
Support rod with hole, stainless steel, 10 cm
Support rod, stainless steel, l = 600 mm, d = 10 mm
Spring balance,transparent, 1 N
Spring balance,transparent, 2 N
Spring balance holder
Quantity
1
2
1
1
1
2
6/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Material
Position Material
1
2
3
4
5
6
Item No.
Quantity
02001-00
02036-01
02037-00
03065-02
03065-03
03065-20
1
2
1
1
1
2
Support base, variable
Support rod with hole, stainless steel, 10 cm
Support rod, stainless steel, l = 600 mm, d = 10 mm
Spring balance,transparent, 1 N
Spring balance,transparent, 2 N
Spring balance holder
Set-up (1/4)
First screw the two support rods together to form a long rod.
Now connect the two halves of the support base with the long support
rod and tighten the locking lever on the left half
Screw connection of the
support rods
Support base with support
rod
7/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Set-up (2/4)
Insert the spring balance holders into the holes of the
short rods.
Spring balance holder in short support rod
Set-up (3/4)
Now place the two support rods in the respective support base halves.
Clamp both force spring balances in place, adjust them to zero and
connect them to their eyelets.
Support rod in base
Experimental setup
8/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Set-up (4/4)
Note:
To adjust the spring balances pull on the weighing
hook of each spring balance several times and then
release it suddenly. If they do not return to zero, you
must adjust them.
Adjustment of the spring balance
Procedure (1/2)
Extend both spring balances successively to about 2/3
of their length.
Observe the effect on your hands.
Deflect spring balance
9/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Procedure (2/2)
Hold the left half of the support base and pull the spring balance apart
with the right one.
Read the scales of both spring balances about every two centimetres and
record the values in Table 1 in the report.
Fixing the support base
Determine about 5 pairs of values.
In the adjacent figure you can see how to name the forces for entering in
table 1.
Correct designation
Report
10/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Monitoring
Which of the following observations is true?
 The left-hand spring balance has displayed the larger value.
 The right-hand spring balance has displayed the larger value.
 Both spring balalces showed the same value.
 Check
Table
Enter your measurement results in the table.
pair Value
Value pair: Value
1N
2 N pair
1
Value pair Value pair
2
Value pair Value pair
3
Value pair Value pair
4
Value pair Value pair
5
11/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Task 1
What do you observe when you attach a spring balance to a fixed object (e.g. table, window)
and pull on it?
 The spring balance cannot be deflected.
 Nothing happens.
 The spring balance displays a value.
 Check
Task 2
Does a spring balance need a holding force?
 No! Holding force is not necessary!
 Yes! A holding force is absolutely necessary!
 Check
12/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de
P0998900
Task 3
Compare the two forces F1 and F2 with
each other. What do you find?
Is it possible to pull out the spring balance
even if one end remains free?
 F2 is twice the size of F1 .
 Yes, even with the free end, it can be pulled
out
 They're the same size.
 F1 is twice the size of F2 .
 No, because it needs a holding power.
 Check
 Check
13/13
Robert-Bosch-Breite 10
37079 Göttingen
Tel.: 0551 604 - 0
Fax: 0551 604 - 107
info@phywe.de
www.phywe.de