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Forces. Static Mechanics. What is a Force?. Pg 24: A force is a push or pull. Also, a force causes an object at rest to start moving and An object that is moving to stop. It can also cause a change in shape and size. Representing a force (pg 24).
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Forces Static Mechanics
What is a Force? • Pg 24: A force is a push or pull. • Also, a force causes an object at rest to start moving and • An object that is moving to stop. • It can also cause a change in shape and size.
Representing a force (pg 24) • An arrow drawn in the direction of the force and • In scale with the magnitude of the force. 10 N A 10 N force can be drawn 10cm long or 5cm long.
Types of forces (pg 24) • Forces are categorised as : Contact or Non- contact . • Contact forces: Frictional, tensional, normal reaction, expansion and compression in springs and upthrust. • Non-contact: Magnetic , gravitational (weight) and electrostatic.
Measuring forces (pg 26) • A spring balance is used. • The unit of force is the Newton (N) • Weight can be calculated: Weight (N) = mass (kg) × g (gravitational field strength) g is usually quoted as 10 ms-2 or 10 Nkg-1 Sometimes more accurately as 9.8
How is weight affected? • Remember weight is due to the pull of gravity. • Therefore weight can vary depending on where you are. • Do you think your mass varies depending on where you are?
Adding forces (pg 28) • Why can forces be added? • Because they are vectors and not scalar.
Forces at an angle • The head to tail method to calculate a resultant which involves lining up the head of the one vector with the tail of the other.
Parallelogram Method • You need a compass and ruler to obtain R. • A protractor is needed to find the angle of the resultant, Θ. Θ can be between A and R or R and B depending on what the question asks.
Forces at 90° • We use Pythagoras’ theorem to find the length of the resultant. • We use trigonometry to find the direction (angle).