VELOCITY AND ACCELERATION
When the body is moving it either moves at constant velocity or it accelarates, or it deccerates. In order to investigate motion of a body, it is neccessary to measure displacement and time of motion. In order to measure these quantities accurately a ticker timer may be used because it can measure small intervals of time accurately.
is the rate of change of displacement (velocity = displacement/time)
is the rate of change of velocity [acceleration is change in velocity/time; a = (v – u)/t]
is the constant rate of change of displacement.
is the constant rate of change of velocity.
due to gravity is the constant rate of change of velocity of a body falling freely under gravitational force only.The ticker timer works by making dots at regular time intervals (constant frequency) on a paper tape running through it.The rate at which the ticker timer makes the dots is the frequency(f)
, which is frequency of the a.c. voltage connected to it.Time between any two dots is equal to the reciprocal of frequency(T=1/f).Time on a ticker tape = number of spaces on the tape divided by frequency of the ticker timer. (t = n/f).From the ticker tape: Velocity = distance occupied by the spaces divided by the time t.
When a tolley is made to move on a runway,friction makes the trolley slow down. To compensate for friction on the runway the runway is inclined until the component of the weight of the trolley along the runway is just enough to overcome the frictional force so that the trolley moves down the runway at constant speed.
In forming the groups and carrying out the activities ensure that the following are deliberately achieved.
- Personal attributes: - motivation and imagination.
- Communication: - Knowing and applying general and specialized vocabulary in physics.
- Team work: - ability to cooperate and share tasks with colleagues.
- Problem solving: - goal focused, seek out relevant information, identify constraints, evaluate alternatives and make decisions/ choices.
- Implementation and application: - the ability to carry out complex operations and follow instructions to achieve accurate results.
- Application of numbers: - ability to work with and present numerical data, using appropriate intermediate calculations.
- Information skills: - ability to present evidence to meet the needs of different audiences using graphs, reports and images.
- Innovation: ability to find a way around a given problem or task, or to improve on the performance of a device.
Motion basic concepts
- Speed is the distance travelled in a given time. For example if a car travels 300km in 5 hours then its:Average Speed = Distance moved/Time = 300/5 = 60 km per hour.
- Velocity is calculated using the same formula, but when the velocity is stated you also have to give the direction of travel. (So Velocity = speed and direction)When the velocity of an object changes, by getting faster or slower, we say there is a change in its acceleration. If a car increases its velocity from 10 miles per hour to 60 miles per hour in 10 seconds then its:
= Change in velocity/Time taken = 50/10 = 5 miles per hour per hour.
Cheetahs can reach a top speed
of between 100 and 120 km/hour.At full speed, a cheetah can cover 7-8 meters every stride and it takes four strides every second.
Question: How many meters will a cheetah cover in a second? Is this its speed or its velocity?
Not only does the cheetah have a high top speed - it also has rapid acceleration
. It can accelerate from zero to 80km per hour in 3 seconds.Although very fast, cheetahs are not as strong as other predators such as a lion or leopard. But additional muscle mass would add to the cheetahs weight and slow it down.
Animal trackers can tell from animal footprints how fast they are travelling and whether they are getting faster or slowing down. When they go faster (accelerate) their footprints get wider apart, and when they slow down (decelerate) their footprints get closer together.Question: When animals go uphill would you expect their footprints to get closer together or further apart? Why?