6. The Moon orbits the Earth at constant speed. Explain why the moon does not have constant velocity. Be specific.
Answers
Earth gravity keep the moon orbiting the earth. keep changing the direction of the moon velocity. this means gravity makes the moon accelerate all the time, even though its speed remains constant.
Orbits and speed/velocity - Higher
When an object moves in a circle at a constant speed, its direction constantly changes. A change in direction causes a change in velocity. This is because velocity is a vector quantity - it has an associated direction as well as a magnitude. A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.
A circle of dotted lines orbiting a point counter-clockwise. This shows the velocity and effects of centripetal force
An object will only accelerate if a resultant force acts on it. For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle.
Example
The moon orbits the Earth and shows the force of gravity on the moon, the direction the moon would travel without Earth's gravity, and the moon's actual orbit.
The Moon orbits the Earth - the diagram shows the force of gravity on the Moon, the direction the Moon would travel without Earth's gravity, and the Moon's actual orbit
Gravitational attraction provides the centripetal force needed to keep planets in orbit around the Sun and all types of satellite in orbit around the Earth. The Earth's gravity keeps the Moon orbiting us. It keeps changing the direction of the Moon's velocity. This means gravity makes the Moon accelerate all the time, even though its speed remains constant.
Describing motion using graphs and equations
The movement of objects can be described using motion graphs and numerical values. These are both used to help in the design of faster and more efficient vehicles
Motion in a straight line
Speed, distance and time
Distance is how far an object moves. It does not include an associated direction, so distance is a scalar quantity. Speed is the rate of change of distance - it is the distance travelled per unit time. Like distance, speed also does not have an associated direction, so it is a scalar quantity.
Typical speeds
When people walk, run, or travel in a car their speed will change. They may speed up, slow down or pause for traffic. The speed at which a person can walk, run or cycle depends on many factors including:
age
terrain
fitness
distance travelled