Forces in action 3.2 Flashcards
What is the equation for Newtons second law?
Force= mass * acceleration
What is weight?
-The force which causes an object to accelerate towards the earths core, this is due to the pull of gravity
-Weight=mass in kg * acceleration of free fall in ms^-2
What is tension?
-Tension is the force experienced by a rope, wire, string or cable that is being supported, hung, pulled and rotated
-Tension can cause objects to change shape or accelerate
What is the normal contact force?
-Known as the reaction force and acts perpendicular to the point of contact.
What is Upthrust?
-The upwards force that a liquid or gas will exert on a body in it, for a liquid this is due to the displaced water.
What is friction?
-Occurs between every two objects in contact and is caused by interatomic and intermolecular forces
-Friction opposes the motion but don’t depend on velocity
What is terminal velocity?
-When the drag becomes equal to the weight of a falling object so the object falls at a constant velocity as there is no resultant force.
When is an object in equilibrium?
-When an object has zero resultant forces;.
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How is a turning moment created and what is the equation for it?
-When a force is applied to an object often perpendicular to the objects axis it causes it to rotate creating a turning moment.
-Turning moment= magnitude of force * perpendicular distance of force from the pivot
What is the principle of moments?
-For an object to be in rotational equilibrium, the sum of the clockwise moment must be equal to the sum of the anticlockwise moment
What is a couple and a torque
-Couple: when two equal antiparallel forces act to produce a rotation
-Torque: The turning effect of a couple
What is the centre of mass?
-Where the whole mass of an object can be thought of as acting, for symmetrical objects finding the centre of mass is easy if the mass is evenly distributed
-The centre of mass can also be located at a point where there is no matter present e.g a horseshoe, this is because the mass is evenly distributed in that spot.
What happens when a force acts through the centre of mass and doesn’t?
-When a force acts directly through the centre of mass the object will either accelerate or move at constant speed in a straight line
-If the force doesn’t act through the centre of mass the object will move with a rotational motion this is because a turning effect has been set up a distance from the centre of mass
What is the centre of gravity?
-Single point where all the weight of an object can be thought to act through
Describe an experiment to find the centre of mass/gravity of an object
- Make three random holes in the object
2.Hang the shape by the first hole and let it come to rest ( a suspended body will always come to rest with its centre of mass directly below it) - Draw a line vertically downwards and repeat for the other two holes
4.Where the lines cross is the centre of mass
How is stability and centre of mass related?
-Objects that have a low centre of mass and wide base area tend to be more stable than those with high centre of mass and small base area
-Objects tend to topple when the centre of mass lies outside the width of the base
What is the equation for density?
p=m/v
How do you calculate the density of regular 3D shapes?
-Work out volume using a ruler and the equation for volume
-Use a mass balance to determine its mass
-Put into the equation p=m/v
What is Archimedes principle?
-The upthrust exerted on an object suspended in water is equal to the weight of fluid displaced
-Therefore an object more dense than the liquid its suspended in will sink and less dense will float
What is pressure? its equation and its units?
-Pressure is the force per unit area and is vector quantity as it has both direction and magnitude
-Pressure=force/area
-The units for pressure are either newtons per square metre or pascals
When is pressure at its highest?
-Small surface area where the force is exerted
-Large force exerted
Why does pressure increase with depth?
-More force is exerted by the weight of the fluid above when you go deeper
