Calculating Average Speed and Energy

Calculating Average Speeds

Describing and Measuring Motion Recognizing Motion Motion An object is in motion when its distance from another object is changing. Ex: Relative to this room, we are not moving; but the Earth moves about 30 km per sec.; so relative to the sun, we are moving very quickly. What example can you think of? Ex: ____________________________

Describing and Measuring Motion Recognizing Motion Reference Point A place or object used for comparison to determine if something is in motion. An object is in motion if it changes position relative to a reference point. (Be careful to make sure that your reference point is basically stationary) Check: When you see a bus moving, what is the reference point? _________

Describing and Measuring Motion Calculating Speed Speed The distance an object travels per unit of time. Speed = Distance / Time Ex: If a car travels 90 km in one hour, the car is traveling at a speed of 90 km/h. Formula Work Answer Units!!! Ex: How many hours will it take a car travelling 60 mph to go 120 miles? _________________________________

Describing and Measuring Motion Calculating Speed Average Speed To find the average speed, divide the total distance traveled by the total time. S = d / t Ex: Suppose a cyclist travels 32 km during the first 2 hrs and 13 km during the next hr. Average speed = d / t = 45 km / 3 hrs = 15 km/hr

The speed of an object at a particular moment in time. Describing and Measuring Motion Calculating Speed Instantaneous Speed The speed of an object at a particular moment in time. S = d / t Ex: A police officer pulls over a driver for going 45 mph in a 35 mph zone. Instantaneous speed was 45 mph Check: Does a car show average speed or Instantaneous speed? _______________

Describing and Measuring Motion

Calculating Potential Energy and Kinetic Energy

Calculating Energy Kinetic Energy Two types of energy Potential Energy

All forms of energy can be in either of two states: States of Energy All forms of energy can be in either of two states: KINETIC ENERGY POTENTIAL ENERGY

What’s the difference? Kinetic Energy is the energy of MOTION Potential Energy is STORED energy.

Kinetic Energy – what does it depend on? The an object moves, the it has. The greater the of a moving object, the it has. Kinetic energy depends on both faster more kinetic energy mass more kinetic energy mass and velocity.

Calculating Kinetic Energy What has a greater affect of kinetic energy, mass or velocity? Why?

What is the unit for Kinetic Energy?  

Some types of Potential Energy include… Gravitational potential energy Elastic potential energy - Stored energy due to - stored energy due to an objects position (height) - depends on mass of the object and its distance from earth. - Stored energy due to compression or expansion of an elastic object

Calculating Potential Energy OR you could multiply weight (in Newton’s) by height

What unit do we use for Potential Energy?  

1. You serve a volleyball with a mass of 2. 1 kg 1. You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s. The ball has ___________ energy. Calculate it.

2. A boy is sitting on his bike at the top of a hill that is 21 m high 2. A boy is sitting on his bike at the top of a hill that is 21 m high. The boy and his bike weigh 20 N. The carriage has ____________ energy. Calculate it.

3. A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. The car has ___________energy. Calculate it.

4. A cinder block is sitting on a platform 20 m high. It weighs 79 N 4. A cinder block is sitting on a platform 20 m high. It weighs 79 N. The block has _____________ energy. Calculate it.

5. A roller coaster is at the top of a 72 m hill and weighs 966 N   5. A roller coaster is at the top of a 72 m hill and weighs 966 N. The coaster (at this moment) has ____________ energy. Calculate it.