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?

• 5 m

• 3 m/s East

• 30 mi North

• 20 degrees Celsius

• Scalar

• Vector

• Vector

• 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.

• vav= The greek symbol delta is read as “change in”

Practice problems1. 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/h12 x 3.6 = 43.2 km/h

• Convert 108 km/h to m/s108 ÷ 3.6 = 30 m/s

Assignment

• Textbook pg. 358 # 1-11