Forces & Pivots. This week you will be: Learning about forces and how to calculate them. Learning about pivots and how to use them

Transcription

1 Loadall Challenge

2 Forces & Pivots This week you will be: Learning about forces and how to calculate them Learning about pivots and how to use them Starting to build your Loadall model

3 Forces - Introduction A Newton (N) is a unit of force You cannot see a force but you can see what it does! It is a push or a pull in any direction How does a Loadall boom use forces? A hydraulic ram is used to push the boom up The force of gravity & hydraulics help to lower the boom Sir Isaac Newton English physicist and mathematician, Founder of the unit of force, the Newton (N). JCB Loadall How the hydraulic ram on a loader boom applies force to raise the load

4 Forces - Mass The mass of an object is the amount of matter it contains The more matter an object contains, the greater its mass Engineers measure mass in kilograms (kg), which is the S.I. unit The mass of an object remains the same wherever it is

5 Force - Weight Weight is the force created by a mass due to gravity The weight of an object can change because gravity strength can change In general: Force (N) = Mass (kg) Acceleration (m/s 2 ) Apply this to weight: Weight = Mass Acceleration by Gravity On earth, acceleration due to gravity is 9.8 m/s² On the moon there is less gravity, so a mass weighs less The astronaut s mass is the same on both the moon and Earth. This is because mass is not effected by gravity. The astronauts weight is less on the moon than it is on Earth. This is because there is less gravity on the moon.

6 Questions Forces Earths acceleration due to gravity: 9.8 m/s² Force (N) = Mass (kg) X Acceleration (m/s²) 1. What is the standard unit of force? 2. A JCB machine has a mass of kg on Earth. What is its mass on the moon? 3. A man standing on weight scales has a mass of 100 kg. How much force is pushing down on the scales? 4. A jug of water rests on a table. It s mass is 5 kg. How much force is pushing down on the table? 5. A crane can lift a force of N what is the maximum mass it can lift on Earth?

7 Answers Forces 1) Newtons 2) kg. Mass is unaffected by gravity 3) Force = Mass Acceleration 100 kg 9.8 m/s² = 980 N 4) Force = Mass Acceleration 5 kg 9.8 m/s² = 49 N 5) Mass = Force Acceleration N 9.8 m/s² = kg

8 Pivots & Levers We can use levers to help us lift things this is called Mechanical Advantage Levers use pivots to multiply the force applied to one end Levers use long arms to multiply the APPLIED force into a larger LIFTING force The position of the pivot affects how much the force is multiplied By using clever positioning of a pivot, we can lift very heavy things with small forces! 1m 5m Pivot

9 Pivots & Levers The lever below is 5 times longer on the applied force side of the pivot than it is on the lifting force side This gives it a lever ratio of 5 Since the lever ratio is 5, the force applied to the longer side is multiplied by 5 on the shorter side The JCB box weighs 500 N and is held with 100 N of force! 100 N 500 N Pivot

10 Pivots & Levers By moving the pivot away from the left side by one extra metre, the lever ratio is reduced to 2 The force applied to the right is now only multiplied by 2 on the left side 100 N 2m 4m 200 N Pivot

11 Pivots & Levers By changing the position of the pivot, the lever ratio is now 2 The force applied to the right is only multiplied by 2 on the left side The 100 N force on the right cannot lift the 500 N JCB box anymore. 100 N 500 N 200 N Pivot

12 Questions Pivots & Levers A Load Effort B Load Effort Mid point pivot Pivot C Load Effort 1. Which lever would require the least force to lift the load? 2. How much force would it take to balance lever A if the load is 10 N? Pivot 3. Which lever would require the most force to lift the load? 4. With B, what would be harder? Picking up the load normally, or using the lever?

13 Answers Pivots & Levers 1. C This lever has the biggest lever ratio, so would multiply your lifting force most 2. 10N A midpoint pivot means that the effort will not be multiplied at all (lever ratio = 1) 3. B This lever has the smallest lever ratio, and would actually reduce your lifting force 4. Using the Lever The pivot is closer to the Effort than the Load, so the lever ratio is less than 1. A lever ratio of less than 1 makes things harder to lift

14 Recap Forces A Newton (N) is the most used unit of force It can be a push or a pull in any direction The mass of an object is the amount of matter it contains It is not affected by gravity Force (N)= Mass (kg) Acceleration (m/s²) Pivots Pivots can be used to lift heavy load with less effort The force needed to lift a heavy load becomes bigger as the pivot point moves away from it

15 Practical Basic Model With your understanding of forces and levers, try to build the most effective basic model possible You should end up with something similar to the picture above