WINTER Templat e 0 1 Are you ready to learn?
Jan 20, 2015
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01
Are you ready to learn?
02
IMPULSE AND IMPULSIVE FORCE
03LEARNING OUTCOMES
• Define impulse and impulsive force
• Explain the effects of increasing or decreasing time of impact on impulsive force
• Describe situations where an impulsive force is beneficial
• Solve problems involving impulsive force
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05
DEMONSTRATION
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06DESIGN AN EXPERIMENTWhat can we do to investigate the impulsive force?
Materials:
Eggs
Newspapers
Sponges
07Relationship between contact
time and force
• Manipulated variables: ??
• Responding variables: ??
• Controlled variables:??
08RESULT & OBSERVATION
Surface types
Contact time
Observation on egg
Force
Table Longer / Shorter
Break / Did not break
Larger / Smaller
Sponge Longer / Shorter
Break / Did not break
Larger / Smaller
tF
1
09Relationship between force and
change in momentum
Before
After
Is the egg experience any changes in momentum?
mupinitial
mvp final
10• So, the change in momentum is:
• What happens to the force when the change of momentum is higher?
initialfinal ppp
mumvp
pF
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11CONCLUSION
-The contact time on impact is affected by the hardness of surface. The harder the surface, the shorter the contact time on impact
-When contact time is shortest, the force of impact will be larger
-The force is directly proportional to the change in momentum
12
• Relationship with impulsive force
• Impulsive force:
• So, the impulsive force is the rate of change of momentum
pF t
F1
t
mumvF
NkgmsF /2
Example:
A bullet of mass 50 g is shot and it travels at a velocity of 100 m/s towards a target and takes 0.01 seconds to come to a stop. What is the impulsive force hitting the target?
• HOW ABOUT IMPULSE?
• Impulse is defined as the changes of momentum
mumvFt
Nskgms /1
Example:
• Figure shows a ball of mass 20 g travelling at 15m/s. It hits a wall and bounces back in opposite direction with a velocity of 12m/s. What is the impulse of the ball?
13APPLICATION OF IMPULSIVE FORCE
Both cars travel at a velocity of 120 m/s and hits a wall. Why does the impact on car A is smaller compared to car B?
A B
• Diagram 2 shows a baseball player wearing a soft thick glove to catch a ball during a baseball match. Compare the impulsive force if the baseball player wears a hard glove to catch the ball.
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• Why a karate expert can break a pile of plank easily using his bare hand?
• Why does food stuff such as garlic can be pounded using mortar and pestle?
15
What are other applications of impulsive force in our daily lives?
Can you explain??
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16Do you want to play some
games?INSTRUCTIONS:
-You are allowed to discuss during the game
-The task for each player is to calculate the questions given
-Given that initial velocity of the ball is 0 ms-1 and mass of the ball is 2 kg. The result of the calculation will determine whether it’s a goal or a miss
17Kick no. Final
velocity (v)
Time of impact
(t/s)
Impulsive force (F/N)
Result of the kick
1 45 0.3 300 GOAL / MISSED
2 25 0.2 250 GOAL / MISSED
3 30 0.6 100 GOAL / MISSED
4 30 0.2 300 GOAL / MISSED
5 30 0.6 100 GOAL / MISSED
6 10 0.8 25 GOAL / MISSED
Initial velocity (u) = 0 m/s
Mass of ball (m) = 2kg
18 What have you learn today?• Impulse as rate of change of momentum
• Impulsive force as the rate of change of momentum in a collision between 2 objects
• Explain the effect of increasing & decreasing time of impact on the magnitude of the impulsive force
• Describe situations and solve problems involving impulsive force
mumvFt
t
mumvF