Y10 Science Forces and Motion Flashcards
What is the unit of force?
N, Newtons
What is the unit of acceleration?
ms^-2, metres per second squared
What is the unit of speed?
ms-1, metres per second
km/h, kilometres per hour
Define acceleration
Acceleration is the rate of change of speed. Acceleration is measured in metres per second per second (m s-2)
Define speed
Speed (v) is a measure of how far an object travels in a period of time.
Speed is measured in metres per second (ms-1)
What do we describe motion?
Speed: Constant speed, stationary. Acceleration: acceleration, deceleration.
Define force
A force is a push or a pull that causes a change in speed, direction or shape
Force (F) is measured in Newtons (N)
What are the contact forces?
Force between two objects that are touching:
Supporting Force
Driving Force/Thrust
Friction Force (Drag/Air Resistance)
Buoyancy
Tension
What is a non-contact force?
Force between two objects that are not touching:
Magnetic Force
Electrostatic Force
Weight Force
What are the common forces?
Electrostatic, magnetic, weight, thrust, friction, drag, buoyancy, lift, tension.
Relate the force acting on an object to its change in speed.
If the mass is kept the same doubling the Force doubles the acceleration.
If mass was the same and force was increased, there would be an increase in acceleration.
Relate the mass of an object to its acceleration
If the force is kept the same, increasing the mass will decrease acceleration (and vice versa)
What does it mean if forces are balanced?
If forces are balanced and the object is stationary the object stays stationary.
If forces are balanced and the object is moving the object moves at a constant speed.
What does it mean if forces are unbalanced?
If forces are unbalanced and the object is stationary the object starts accelerating (and moving).
If forces are unbalanced and the object is moving the object accelerates OR decelerates
What does the direction of the net force mean?
If the direction of the net force is the same as the direction of motion, the object accelerates.
If the direction of the net force is in the opposite of the direction of motion, the object decelerates.
Define friction
Friction is a contact force that opposes motion. Friction always generates heat. The direction of this force of friction is always opposite to the direction in which the object or surface is moving.
How do you increase or decrease friction?
Increasing friction:
Make the surface area rougher.
Make the surface area dry.
Decreasing friction:
Make the surface area in contact smaller.
Make the surface area smoother.
Apply a lubricant (oil, water) between the surfaces to reduce surface contact.
Streamline the object to reduce the object’s cross-sectional surface area.
What is the effect of friction on objects?
Friction causes objects to heat up and to wear away at their surfaces. Without friction, the tyres of a car would not grip the road.
How do you increase or decrease drag, relate this to an object’s cross-sectional surface area, and to its speed through the air.
Increasing drag force by increasing an object’s cross-sectional surface area: When the parachute opens, its surface area increases. This means that there is a larger area moving through the air, so there is more drag. This increases the relative size of the upwards force.
Decreasing drag force by decreasing an object’s cross-sectional surface area: An aeroplane is shape designed to reduce the object’s cross sectional surface area and therefore reduce the amount of drag.
What is the difference between mass and weight?
Mass is the amount of matter in an object. It is measured in grams or kilograms.
Weight is the force of gravity acting on an object. It is measured in newtons.
Gannet question (just thought i should know this.)
The forces acting on the gannet midway through the dive are weight force downward and air resistance/friction/drag upwards. As an object’s speed increases the strength of the friction force acting to oppose the movement will also increase. There is a change in acceleration when the gannet tucks its wings in as the surface area of the gannet exposed to the air will decrease, meaning that the strength of the friction force acting upwards against the weight force will also decrease. This means that the weight force and friction force will be unbalanced, there will be an increase in the net force downwards, and the gannet will have an increase in acceleration. The gannet will not keep accelerating as one of two things will happen : it will reach terminal velocity (highly unlikely) or it will hit the water.
If it reaches terminal velocity then that is because the friction force has equalled the weight force (increasing speed will increase friction) and thus the forces are balanced, there is no net force, and the gannet will stop accelerating and travel at a constant speed. If it hits the water then the buoyancy force will be greater than the weight force (the displaced water particles will act to push upwards against the gannet as it enters the water) meaning forces will be unbalanced and there will be a net force upwards causing the gannet to stop accelerating and slow down.
