Lesson 11 Chapter 4

• Physics
• Middelbare school
• vwo
• Leerjaar 3

Force and motion

This lesson

• Quick recap
• Discussing the homework
• Newtons first & second law
• free fall
• acceleration due to gravity
• studying

Quick recap

Distance-time graph — speed-time graphs

Distance-time graph — speed-time graphs

Distance-time graph — speed-time graphs

Shows:

• the distance traveled.
• The gradient of the graph shows the speed of the motion.

Which of the two is faster?

•  The gradient of the slope shows the speed of a movement
•  blue is faster

Distance-time graph — speed-time graphs

Shows:

• the speed something is traveling it.
• The gradient of the graph shows the acceleration.
• The area under the graph gives you the distance covered.

Lesson 10 Chapter 4

Key formula's for force and movement.

v=​t​​d​​

a=​t​​v​f​​−v​i​​​​

Speed

acceleration

Homework exercises

physical quanitity	Symbol for the physical quantity	unit	symbol for unit
distance
		seconds
		meter/second
	Δv
accelration
			kg
	F
displacement
Work

physical quanitity	Symbol for the physical quantity	unit	symbol for unit
distance	d	meters	m
time	t	seconds	s
speed	v	meter/second	m/s
change in speed	Δv	meter/second	m/s
accelration	a	meter/second squared	m/s 2
mass	m	kilogram	kg
force	F	Newton	N
displacement	s	meter	m
Work	W	Newton- meter	Nm

Newtons First law of motion

Newtons second law of motion

Newtons first law

Inertia

An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

Link

Newtons second law

Link

F​res​​=m⋅a

Newtons second law

Link

F​res​​=m⋅a

Fres : resultant force — Newton (N)

m: mass — kilogram (kg)

a: acceleration — m/s2

Newtons second law

Link

F​res​​=m⋅a

a=​m​​Fres​​

Fres : resultant force — Newton (N)

m: mass — kilogram (kg)

a: acceleration — m/s2

Free Fall

Falling in the air

Practice problem

A professional cyclist with a mass of 85 kg goes from cycling at a regular speed to sprinting. A trainer is measuring their speed. At moment 1 they're cycling at a speed of 8.8 m/s. at moment 2, 7.6 seconds later they're cycling at a speed of 11.9 m/s.

The magnitude of the combined resistive forces of friction and air resistance during this acceleration have a magnitude of 41 Newton. Calculate the magnitude of the foward force the cyclist applies by paddling to oppose these resistive forces

A professional cyclist with a mass of 85 kg goes from cycling at a regular speed to sprinting. A trainer is measuring their speed. At moment 1 they're cycling at a speed of 8.8 m/s. at moment 2, 7.6 seconds later they're cycling at a speed of 11.9 m/s.

The magnitude of the combined resistive forces of friction and air resistance during this acceleration have a magnitude of 41 Newton. Calculate the magnitude of the foward force the cyclist applies by paddling to oppose these resistive forces

Given

m_cyclist = 85 kg

v_i = 8.8 m/s

v_f = 11.9 m/s

t_acceleration = 7.6 s

F_{resistive forces} = 41 N

Asked

the magnitude of the forward force the cylists generates.

Working

a=​Δt​​Δv​​

a=​7.6​​11.9−8.8​​=0.4079​s​2​​​​m​​

F​res​​=m⋅a

F​res​​=85⋅0.4079=34.6711N

F​forward​​=F​res​​+F​resistive​​

F​forward​​=34.6711+41=75.67N