1. What force is needed to keep a 5 kg
mass moving at a constant velocity of
10 ms-1?
2. Calculate the force needed to
accelerate a 8 kg mass at 2 ms-2
3. Calculate the acceleration of the mass
shown below.
A
D
B
C
Sketch labelled vector diagrams to show:
1.
2.
3.
4.
A+B
B+A
B+D
B+C
Tutorials – 2 hours (expected)
Franky – Friday after school
Will K – Friday after school
Jakob – Friday after school
Jacob – Friday after school
Will S – Friday after school
David – Friday lunch time (50 min)
Sam – Sunday 10am
Scott – Sunday 10am
Tim –
Yesterday’s Lab… “Terminal Velocity”
•
Do not expect any assistance or
guidance from the teacher during the
actual assessment
•
Read the aim – this is the big picture
(To find the relationship between…)
•
Read thoroughly and follow every
instruction very precisely
Yesterday’s Lab… “Terminal Velocity”
•
Read, read, read… and read more
•
Analysis – calculate the terminal
velocity?
•
Finish the lab write-up by Tomorrow
•
Tutorial – Lunch time today
What is force?
• Force is “push or pull”
• Force is a vector
•
Measured in N (Newtons)
Examples of Forces
• Thrust Force (an accelerating car)
• Buoyancy Force (a floating ship)
• Lift Force (a flying plane)
• Tension Force (springs, ropes, BOTH ENDS)
• Friction Force (against movement)
• Weight Force (always downwards)
• Support Force (usually upwards)
What happens when force
is applied to an object?
• It moves
• It “accelerates”
Can anything be moving without
any force being applied on it?
• no force = stationary
• no force = no acceleration
Force
♥
Acceleration
Force causes acceleration
But how come Frankie is not
moving or accelerating?
Because the “Net Force” is zero.
Net force = the sum of all forces
Note: Net force is also known as
Resultant force or Total force.
3N
10N
Box
10N
3N
Sketch labelled vector diagrams to show
the net force being applied to the box.
3N
5N
Box
10N
2N
Sketch a labelled vector diagrams to
show the net force being applied to
the box.
Net force = the sum of all forces, also
called resultant force or total force.
Newton’s
st
1
Law:
If the net force on an object is zero,
the acceleration will be zero.
Zero acceleration means the velocity
of the object is constant.
Newton’s 2nd Law:
If the net force on an object is NOT
zero, the acceleration will NOT be zero.
The relationship between Fnet and the
acceleration is:
Fnet = ma
(m = mass)
Both Fnet and a will always be in the
same direction.
A tow truck pulls a car of mass 1250 kg
with a force of 1500 N. The friction
between the truck and the road is 600N.
a) Sketch a vector diagram to show the
net force.
b) Calculate the car’s acceleration.
c) Once the car starts moving, what
would happen if the two truck pulls
with a smaller force of only 600N?
Q: What is your weight?
Q: What is your mass?
Weight = Mass
Weight is a type of force,
measured in Newtons
Fw = mg
g is the acceleration due to gravity
g = 9.8 ms-2 everywhere on the surface of
the Earth
Mr Chu’s “coin drop” theory
Question:
Should Mr Chu be
charged of an
attempted
manslaughter?
A parachutist of mass 100 kg (including
parachute) jumps from a great height.
After a few seconds she reaches a
terminal velocity of 50 ms-1.
a) What is the parachutist’s total
weight?
b) What is the force of air resistance
on her at terminal velocity?
The parachutist now pulls her ripcord
and as her parachute unfurls she slows
to a steady speed of 5.0 ms-1 in 2.0
seconds.
a) Calculate the acceleration over the
2 seconds.
b) Calculate the net force acting on
her over the 2 seconds.
c) What is the force of air resistance
now?
What if there was no air
resistance?
Free fall = unlimited speed?
Newton’s 3rd Law:
For every action force there is
an equal and opposite reaction
force. (eg. a gun recoil)
Homework Booklet Sheet #5
Q 1 ~ 9 (except for Q5)
Purple Worksheets pg. 52 ~ 54
Activity 9A – textbook pg. 109