Forces in Action

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Forces are needed to
stop, start, accelerate or decelerate
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Resultant force means
Acceleration and forces arent balanced. Vector sum of all forces
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Equilibrium means
not accelerating and forces are balanced
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Free body diagrams dont include
the force the object exerts on the rest of the world
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4 Examples of forces (vector quantities)
Weight, Normal contact force (reaction), Tension, Friction
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Acceleration is proportional to? Acceleration is independent of? and state units of acceleration
Force. Mass. acceleration = ms-2
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Resolve a force by
Splitting it into components (VECTORS)
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Three forces acting on a point in equilibrium...
form a triangle
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drawing forces in vector addition
vector arrows 'tip to tail'
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The mass of a body makes it resist Changes in motion. What does increasing mass do to its inertia
greatens it (greater resistance to a change in velocity) (gravitational field strength doestn affect mass)
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What is weight?
W=mg. The force experienced by a mass due to a gravitational field.
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Define center of mass
the single point that you can consider an objects whole weight to act through. Balances around this point. (plumbline experiment)
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Define friction and state the two types
a force that opposes motion. Converts kinetic energy into heat. Contact (solid) and Fluid (drag - liquid and gas)
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Fluid friction depends on
viscosity (higher V lower TV), speed, shape/size
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The heavier an object is, the faster it reaches terminal velocity (drag). An object reaches terminal velocity when
Friction force = Driving force (works for water aswell)
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Density doesnt vary with size or shape. Define Density and state its units
mass per unit volume kgm-3. An object will float if it has a lower density than that of the liquid.
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Define Pressure and state units
Force per unit area Pa / Nm-2. Also P=hpg (h is depth, p is density of fluid, g is acceleration due to gravity)
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Explain Upthrust
upwards force that fluids exert on objects that are submerged. P=hpg and the top and the bottom of the object are at different depths. Upthrust = Weight of fluid displaced
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Define a moment/torque
the turning effect of a force. Moment (Nm) = force (N) x perpendicular distance from pivot (m)
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State the principle of moments
for a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point
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What does the effort force do in a lever
acts against a load force by means of a rigid object rotating around a pivot
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Define a couple
a pair of forces of equal size which act parallel to each other but in different directions
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A couple doesnt produce any resultant linear force, what does it produce and what is the equation?
a turning force.Torque of a couple (Nm) = size of one of the forces (N) x perpendicular distance between the forces (m)
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Card 2


Resultant force means


Acceleration and forces arent balanced. Vector sum of all forces

Card 3


Equilibrium means


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Card 4


Free body diagrams dont include


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Card 5


4 Examples of forces (vector quantities)


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