Download Science 20F: Unit 2

Science 20F: Unit 2
Physics: In Motion
Physics, Matter and Energy
• Physics is the science that deals with matter
and energy and motion and force
• Matter is anything that takes up space and has
mass. ( basically everything other than energy)
• Energy is the ability to do work. There are
several different types of energy( kinetic,
potential, light, sound , heat, nuclear..)
Kinematics
• Motion is defined as the movement of an object,
or any of its parts, from one place to another.
• The study of the motion of objects and the forces
that affect their motion is called mechanics.
• Mechanics is divided up into two distinct
categories:
– Kinematics
– Dynamics
• Kinematics is the science of describing the
motion of objects using words, diagrams,
numbers, graphs, and equations.
• The goal of any study of kinematics is to
develop models that help us in explaining the
motion of real-world objects.
Scalars and Vectors
• Scalars are quantities which are fully
described by a magnitude alone.
• Vectors are quantities which are fully
described by both a magnitude and a
direction.
Scalar or Vector?
• 5m
• Scalar
• 3 m/s East
• Vector
• 30 mi North
• Vector
• 20 degrees Celsius
• Scalar
• Distance is a scalar quantity which refers to
"how much ground an object has covered"
during its motion.
• SI units for distance are metres (m)
• Time is the duration between two events
• SI units for time are seconds (s)
Speed
• Speed is a scalar quantity referring to how fast an
object is moving. A fast-moving object has a high
speed while a slow-moving object has a low
speed. An object with no movement at all has a
zero speed
• Often measured in m/s or km/h
• The average speed of an object is determined by
taking the distance travelled and dividing it by the
total time taken.
•
Δ𝑑
vav=
Δ𝑡
The greek symbol delta is read as
“change in”
Practice problems
1. A frog hops 3.5 m in 7 s what is its average speed
in m/s.
2. A racecar completes 3 laps of a 3.5km oval track in
3 minutes. Find its average speed in km/h.
3. Zdeno Chara’s slapshot travels at 48 m/s. If he
shoots a puck at Joey who is standing 24m away,
how much time does Joey have to get out of the
way?
Practice problem
• Connor misses the bus and has to walk to
school (now he is late for science class) the
distance he walks is 6.4 km and it takes him 45
min. What is his average speed in km/h?
Instantaneous Speed
• Is the speed at which an object is travelling at a
particular instant
• An example is the reading on your speedometer
• Police radar measures instantaneous speed
• High instantaneous speeds
make traffic accidents more
serious
Constant Speed
• If an object’s instantaneous speed remains the
same, we say it is travelling with constant
speed or uniform motion.
• Cruise control keeps the motion of your
vehicle uniform
• Average speed of an object will be the same
as its instantaneous speed if it is travelling at a
constant speed
Conversions
• 1 m/s = 3.6 km/h
• 1h = 3600 s
• Therefore at 1 m/s in 1h you would have
travelled 3600 m which is 3.6 km.
• To convert m/s – km/h times by 3.6
• To convert km/h – m/s divide by 3.6
Practice
• Convert 12 m/s to km/h
12 x 3.6 = 43.2 km/h
• Convert 108 km/h to m/s
108 ÷ 3.6 = 30 m/s
Assignment
• Textbook pg. 358 # 1-11