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.

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

CBD

Sketch labelled vector diagrams to show:

1. A + B2. B + A3. B + D4. B + C

Tutorials – 2 hours (expected)

Franky – Friday after schoolWill K – Friday after schoolJakob – Friday after schoolJacob – Friday after schoolWill S – Friday after schoolDavid – Friday lunch time (50 min)Sam – Sunday 10amScott – Sunday 10amTim –

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.

10N

Sketch labelled vector diagrams to show the net force being applied to the box.

10N

3N

3N

Box

5N

Sketch a labelled vector diagrams to show the net force being applied to the box.

10N

2N

3N

Box

Net force = the sum of all forces, also called resultant force or total force.

Newton’s 1st 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 = MassWeight is a type of force,

measured in Newtons

Fw = mgg is the acceleration due to gravityg = 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 #5Q 1 ~ 9 (except for Q5)

Purple Worksheets pg. 52 ~ 54

Activity 9A – textbook pg. 109